Aguablanca Dike along the Cauca River, Cali, Colombia

Transcription

1 Aguablanca Dike along the Cauca River, Cali, Colombia Diagnosis and recommendations Final NL Agency The Netherlands Ministry of Foreign Affairs / Colombia Transition Facility January 2013

2 Aguablanca Dike along the Cauca River, Cali, Colombia Diagnosis and recommendations Final file : BB2984 registration number : LW-AF version : final classification : NL Agency The Netherlands Ministry of Foreign Affairs / Colombia Transition Facility January 2013 HaskoningDHV Nederland B.V. No part of these specifications/printed matter may be reproduced and/or published by print, photocopy, microfilm or by any other means, without the prior written permission of HaskoningDHV Nederland B.V..; nor may they be used, without such permission, for any purposes other than that for which they were produced. The quality management system of HaskoningDHV Nederland B.V.has been approved against ISO 9001.

3 CONTENTS PAGE EXECUTIVE SUMMARY 3 1 INTRODUCTION Extreme rainfall in Colombia has led to alarm for possible dike failure Scope of work Project team 8 2 HYDROLOGY AND HYDRODYNAMIC MODELLING Discharge of Rio Cauca under influence of Salvajina reservoir Analysis of extremes leads to lower expected maxima than previously calculated Identification of dike locations with critical elevation level Flood modelling results 12 3 FLOOD RISK MANAGEMENT: COST OPTIMIZATION 13 4 IMPROVEMENT OF DIKE SAFETY, IMMEDIATE AND SHORT-TERM STRATEGY Analysis of present conditions Dike crest level of the main dike Dike conditions of Canal Sur and Rio Cali Water levels and river bed management Freeboard discussion Dike strength Immediate and short term strategy Immediate actions Short-term strategy LONG-TERM APPROACH FOR FLOOD PROTECTION CALI Anticipate on impact of economic and regional developments and possible climate change effects Spatial developments Economic development Climate change Ongoing and increased need for flood protection Risk based approach for flood protection for Cali Combination of flood risk and earthquake risk Strategies for maintaining and improving flood protection Flood protection level Strategy 1: Controlled retention upstream of Cali and on east bank Strategy 2: Total reliance on Jarillón Aguablanca Choice of strategy 26 6 GOVERNANCE AND WATER AUTHORITY 27 7 REFERENCES 28 ABBREVIATIONS 30 8 COLOPHON 31 NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

4 APPENDICES 1 Hydrology 2 Longitudinal dike profiles and hydrodynamic modelling results 3 Hydrodynamic modelling, methodology 4 Flood risk management methodology 5 Field assessment of the conditions of the Aguablanca dike 6 Structural stability and analysis of failure mechanisms 7 Inspection plan 8 Water governance and regional water authorities in the Netherlands (partially derived from [14]) 9 Ownership of the Aguablanca dike 10 Table of damage and investment costs NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

5 EXECUTIVE SUMMARY Commissioned by Agency NL 1, Royal HaskoningDHV in collaboration with Colombian consultant Corporación OSSO, and supported with input by Dutch Waterboard Aa and Maas has made an analysis of the status of the Aguablanca Dike along the Cauca River near Cali, and elaborated recommendations for a short and long term strategy to improve its safety level. Our main conclusions are the following: 1. The Aguablanca Dike is basically a good dike, but enforcement and maintenance of the dike and river profile over the past 50 years has been insufficient. This lack of maintenance leads to a number of immediate and short term measures to be taken. 2. The protected area has developed over 50 years from an agricultural area into a densely populated urban area. This leads to the necessity for an increase in flood protection level as a long term objective. 3. Legally, at least until October 2012, CVC has been owner of the dike since its construction, but responsibility for maintenance and control of the dike are not transparent. Ad. 1 The present state of river flood protection of Cali has fallen below the standard of the original dike design of the Aguablanca Dike in 1958 (T= m freeboard). With relatively limited effort this original flood protection can be restored. The short-term strategy 0 (reference strategy) is aimed at this original protection. A serious point of attention is the lack of maintenance of the main pumping station in the dike body. Immediate action is required to repair a number of the outer valves that are essential for flood prevention, before a threatening situation may occur. EMCALI is owner of this pumping station. Ad. 2 Since 1958, 700,000 to 800,000 people have come to live and work in the flood prone area of Cali. Therefore the flood protection of these people and there economic activities needs to increase. In other words, the Jarillón Aguablanca needs to be raised and strengthened. Ad. 3 We have verified that, at least until recently, CVC has been the legal owner of the dike (see Annex 9). During presentation of the results of this study on December 7, 2012, it came to our attention that CVC may have signed away its ownership to the City of Cali during October or November 2012, but this has not been verified through documents. Anyhow, more organisations are involved in decisions regarding constructions on and near the dike. In this situation it is not transparent which organisation has ultimate responsibility for the dike, leading to a questionable lack of maintenance and increase of inundation risk. To have a solid defence against inundation from the Cauca River, it is a prerequisite to have only one organisation ultimately responsible for control of the dike. Over the years, the involvement of CVC in maintenance and control of the dike has diminished. Various structures in the dike body belong to other 1 Financed through the Transition Facility which is supported by the Ministry of Economic Affairs, Agriculture and Innovation and the Ministry of Foreign Affairs NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

6 entities like EMCALI and DAGMA. The different authorities lack communication on important issues of design of new constructions and maintenance issues. We have defined an action plan including technical and non-technical issuesactions to be taken and strategies to follow. Tabel 1 Urgent: Action plan 1. Rehabilitation of pumping station The condition of the closing systems of the pumping station Paso del Comercio is alarming. They are either out of order or malfunctioning. Immediate action to repair broken or malfunctioning valves is required to ensure maximum flood protection. This action cannot be postponed Rehabilitate 6 critical points in the Aguablanca dike and low points in the dike of Canal Interceptor Sur Where the dike crest level is the most important parameter in flood protection, immediate action is recommended to rehabilitate the lowest points in the Aguablanca dike : 1 km km km km km km In addition it is recommended to rehabilitate the low points of the dike of Canal Interceptor Sur, which have been identified in the longitudinal profile of Annex Remove ant nests and fill the cavities caused by these nests The cavities of ant nests (hormiga arriera) need to be filled. Shallow nest cavities can easily be repaired by digging out and applying new clay filling. Deeper nests should be filled, preferably with bentonite. Short term: 1. Raise the security level of the dike We recommend a security level for a return period of 500 years with a freeboard of 0.5 m. The extra costs for a safety level with a return period of 500 years as compared to 100 years are relatively small. 2. Resettlement of house on the dike and in the berm of the dike Approximately families are living on the dike and berm which need to be resettled. 3. Install by law one entity with ultimate responsibility for the dike This entity should have responsibility for maintenance, inspection and supervision of all construction in the dike, and have the technical and financial resources to perform its task properly. 4. Introduce a maintenance system Develop a system for maintenance of the dike, including norms for interventions, constructions, housing, 2 In a letter to Dr. M. Guerrero, the Mayor of Cali, dated December 17, 2012, EMCALI has confirmed that it is envisaged to repair the damaged valves in January 2013 NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

7 industries and a plan for periodic inspection. 5. Evaluate existing plans for dike re-enforcement There are existing plans by EMCALI for dike re-enforcement around the drinking water plant. We recommend an evaluation of these plans in cooperation with CVC and investigate alternatives in order to reduce costs. 6. Control further spreading of the ant species Arriera Regular inspection should be aimed at eradication of the ants. Ant nests should be dug out as soon as observed. 7. Action for river bed and flood plain maintenance and construction debris control Enforcement of river bed maintenance needs to be improved. This is on one hand predominantly a government issue, on the other hand economical incentives and technical possibilities can help. Especially the dumping of construction debris needs to be stopped. 8. Review the operation rules of the Salvajina reservoir We recommend a review of the operation rules to attempt a further optimization of compliance with the different objectives of the reservoir, i.e. reduce peak discharge, supply a certain minimum discharge for environmental purposes and produce energy. This will require a simulation study based on historic discharges, where we suggest to use stochastic modelling and use of generated synthetic time series. A special point of focus is the time scale to be used, and possible use of meteorological forecasting. Medium term and long term: 1. Improve land use planning Water safety should be a leading principle in an integral approach of land use planning by the municipality and regional authorities. It is therefore an important issue related to the institutional issues. Enforcement of spatial management and assessment of spatial developments on consistency with the long-term flood approach needs to be implemented. The analysis of this study should be incorporated into the land use planning strategy of the municipality. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

8 In addition to the action plan, we have the following recommendations: 1. Research into climate change effects We recommend further research into the effects of the trend in the ONI (Oceanic Niño Index) on extremes of the Cauca river discharge. 2. Research into fluvial morphodynamics We recommend that the fluvial morphodynamics of the river Cauca be studied in order to have a better understanding of its morphodynamics and the influence of the human activities on the morphological developments. 3. Further research into river hydrodynamics Develop an integrated hydrodynamic model of the river Cauca starting at Salvajina reservoir. In this model the overtopping and flooding should be included. The model should be calibrated in order to reproduce the last flooding events for instance by comparing the inundated area with aerial photographs. We have understood that this model will be constructed in another project [5] and advise the local team to participate in this study. 4. More soil investigation for strength parameters related to dike slope stability We recommend doing more triaxial tests on undisturbed clay samples of the dike body to gain a better insight into the strength parameters along the profile of the Aguablanca dike. We suggest making and executing a detailed plan, based on a number of indicative borings. 5. River bed and flood plain maintenance and construction debris control Enforcement of river bed maintenance needs to be improved. This is on one hand predominantly a government issue, on the other hand economical incentives and technical possibilities can help. Especially the dumping of construction debris needs to be stopped. A strong recommendation is to invest in debris crusher systems to convert waste debris into raw construction materials, ready for re-use. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

9 1 INTRODUCTION 1.1 Extreme rainfall in Colombia has led to alarm for possible dike failure Extreme rainfall in 2010 and 2011 has resulted in extreme river discharges and water levels in various river basins in Colombia and has disrupted the lives of more than three million Colombians, uprooted thousands from their homes and destroyed swathes of farmland. In Cali, the threat of a possible breach of the existing dike system has alarmed the highest authorities. The impact of such a breach on the city and the country has led President Santos to put urgent action to improve the Aguablanca Dike protecting the city as top priority. The Aguablanca Dike along the Cauca River in the municipality of Cali has a length of approximately 17 km. It is the only structural flood protection of the city of Cali against floods from the Cauca River. Juanchito Figure 1 Schematic situation of Aguablanca Dike together with dike of Canal Interceptor The dike was originally built in the late 50 s and early 60 s in order to habilitate the Aguablanca s low lands for agricultural purposes. However these areas have witnessed significant urban development. During the last four decades the city has spread towards the river. Dwellings have been built on the dike crest, as well as in the floodplain. Today almost 20% of the population of the city is settled in flood plain and around people live directly over the dike structure. The largest water treatment plant that supplies around 60% of the city is also located in this area. The main pumping station of the city, Paso del Comercio, is located in the lowest part of the city at the end of the principal drain channel. A population of over people in the District Aguablanca is currently at risk from flooding. Climate change and progressive anthropogenic impacts in the upper basin of the Cauca River will only further increase these risks. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

10 1.2 Scope of work The scope of work has included the following activities: 1. Assessment of the physical condition and structural stability of the current dike. This includes: a field survey over a distance of 18 km; application of geotechnical software; review of previous surveys of the dike; training of the Colombian engineers of CVC during the process of dike inspection 2. Calculations using a hydrodynamic model to model inundations of different frequencies (1:100 year 1:250 year, 1:500 year). 3. Estimation of the optimum dike height in terms of the costs of dike improvement and the flood damage avoided. 4. Development of action plan and strategies for short term an medium term measures 5. Prioritization of sections of the dike that should be reinforced. 6. Organisation of a workshop with presentations of dike management in the Netherlands, preliminary results of the inspection of the Aguablanca Dike, presentation of a dike inspection manual in Spanish. 1.3 Project team The project team consisted of the following persons: Hans Leenen (Royal HaskoningDHV): team leader and senior expert in hydrology and risk management Michel Tonneijck (Royal HaskoningDHV): senior dike expert Marcela Busnelli (Royal HaskoningDHV): senior expert in hydrodynamic and morphological modelling Steven Sjenitzer (Royal HaskoningDHV): geotechnical expert Joop de Bijl (Waterboard Aa and Maas): senior dike expert. For this project Joop de Bijl of Waterboard Aa and Maas has participated to include expertise of a leading Dutch Waterboard. Royal HaskoningDHV has collaborated with Colombian counterpart Corporación OSSO in Cali, whom we greatly thank for its professional and kind cooperation. Team members of OSSO were: Carlos Regalado, geotechnical engineer and outstanding help in translation issues Angela Cabal, specialist in hydraulic modelling Jorge Mendoza, civil engineer Henry Peralta, general coordinator Andres Velasquez, socio-economist NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

11 2 HYDROLOGY AND HYDRODYNAMIC MODELLING 2.1 Discharge of Rio Cauca under influence of Salvajina reservoir The discharge of the Cauca River along the Aguablanca dike is influenced by the operation of the Salvajina Dam, 139 km upstream of the hydrometric station of Juanchito (Figure 2). Juanchito is the most important hydrometric station along the Aguablanca dike with water level data going back to 1934 and a continuous time series since The Salvajina reservoir was put into operation in 1985 and is a multipurpose reservoir with the objectives of energy production and attenuating flood peaks on the Cauca River. Figure 2 Location of Salvajina Reservoir The operation rules of Salvajina Reservoir are primarily on a monthly basis (but may be adjusted daily) and are controlled by the Committee of Operation. Decisions are agreed upon by CVC and EPSA (Empresa de energía del Pacífico S.A.). During the first days of each month the Committee defines the water release for the month based on a set of operation rules, which will not be treated here in detail [1]. The monthly strategy will be maintained as much as possible, but may be modified on a daily basis. One objective is to maintain the discharge at Juanchito station between 130 m 3 /s and 900 m 3 /s. The objective of the minimum NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

12 flow is dilution of contamination. This flow can be regarded as an environmental flow. The envisaged maximum flow provides a safe level against inundations by overtopping of the Aguablanca dike. As observed in recent years, the applied operation of Salvajina has not been able to prevent much higher flows at Juanchito station (see Annex 1) of up to an estimated discharge of 1148 m 3 /s in The operation of Salvajina reservoir does not have strict optimization rules. We recommend a study to optimize the operation regime, by applying simulation modelling of the reservoir using stochastic methods, for instance with synthetic flow generation based on a Thomas-Fiering model. Such a modelling effort should take into account the different conflicting objectives of the reservoir, i.e. generating energy on one side, reducing flood peaks on the other, and also allowing for a certain environmental flow. 2.2 Analysis of extremes leads to lower expected maxima than previously calculated In order to evaluate dike safety on the long term, it is common practice to apply a statistical approach on existing data (Appendix 1) and determine return periods for different discharges, based on the best fit of a certain probability function. This has also been done in previous studies, a.o. by the Universidad del Valle [2]. To define return periods and discharges for the present conditions the data of water levels and related discharges at Juanchito before 1985 cannot be used because of the influence of Salvajina reservoir. So only the years since 1985 have been used in the analysis of return periods. The Universidad del Valle [2] has applied a Gumbel distribution to the data, resulting in higher discharge data for return periods of 25 years and more, than what is calculated under the present study. The reason for the differences is that the Gumbel distribution gives a rather poor fit to the data. Under the present study a number of probability distributions have been compared for quality of fitting the data. The Log Pearson 3 provided the best fit, based on statistical grounds (K-S statistic, see Table 2). A quick way to assess the applicability of various probability functions is the so-called Moment-Ratio diagram, which shows differences between statistical characteristics of the observed values and the theoretical distributions. (see Moment-Ratio diagram in Annex 1). From this diagram it is clear that the Gumbel distribution is not suitable in this particular case. Table 1 shows the differences that occur for return periods higher than 25 years. The difference between the discharges for the return period of 100 years leads to a difference in water level of 0.67 m according to the current calibration table for the level-discharge relationship (Annex 1). Our conclusion is that previous studies have overestimated the discharges related return periods above 25 years. As a basis for the hydrodynamic modelling the present study will apply the results from the Log Pearson 3 distribution as presented in Table 1, graphically presented in Figure 3. Table 1 Return period Comparison of estimated return periods (station Juanchito) with previous studies Ref. [2]: Gumbel distribution Discharge [m 3 /s] Present study: Log Pearson 3 distribution Discharge [m 3 /s] NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

13 Return period estimates: Extreme discharges Juanchito-since 1985 [m3/s] Observed Gumbel Weibull LP3 Normal LN2 Gamma Logistic LN Return period [time units] Figure 3 Return period estimates for extreme discharges at Juanchito Table 2 Kolmogorov Smirnov test statistic Probability function KS-Statistic KS-critic (0.10) LP Weibull LN Gumbel NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

14 2.3 Identification of dike locations with critical elevation level The discharge data as extrapolated with the LP3 distribution (Table 1) have been used to estimate the water levels along the Aguablanca dike for various return periods. The Universidad de Valle [2] applied a one dimensional model to estimate water levels for different return periods. In all modelling efforts, the right bank of the Cauca River has been modelled as an infinitely high wall without inundation possibility. These levels have been used as input for the estimation. In this estimation Juanchito station has been used as a reference to adjust all levels along the Aguablanca dike accordingly. The water levels associated with different return periods have been compared with the latest longitudinal dike profile, measured in 2012 (Annex 2). In doing so, the critical points along the dike in terms of level, were identified: 1 km km km km km km Based on these critical points inundation simulations were carried out with the 2D-model CCHE2D of the University of Mississippi to establish a basis for damage estimates (see Annex 2). 2.4 Flood modelling results The 2D-model CCHE2D of the University of Mississippi of the river Cauca (between the Canal Interceptor Sur and the river Cali) has been applied in this study [3]. The model was recalibrated based on the updated statistics of discharges and water levels. The hydrodynamic model provides insight in flood characteristics, such as water depth and flow velocity. Three scenarios were defined and simulated as input for the risk management assessment (Chapter 3): Flooding due to breaking by overtopping for a return period of 1:100, 1:250 and 1:500. The graphical results of the computations for a return period of 1:100 are presented in Annex 2. Numerical results of the computations are presented in Table 3. These flooding characteristics have been applied in the risk-based analysis to obtain the damage costs corresponding to a certain flooding probability. Table 3 Characteristics flooding scenarios Return period Maximum inundated area [km 2 ] NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

15 3 FLOOD RISK MANAGEMENT: COST OPTIMIZATION Initial costs of relocation of dike dwellings play an important role in total costs In this study we apply the principles used in the Netherlands for risk-based design of flood protection systems to the Aguablanca area. In this economic optimization, the investments in more safety are balanced with the reduction of the risk to find an optimal level of flood protection. We have assumed that the dike will only fail because of overtopping. The strength of the dike is subsequently designed in such a way that the dike does not fail at water levels below the design water level, for all possible failure mechanisms such as piping and lack of stability. The assessment of the physical conditions and structural stability of the dike is described in detail in Annex 5, and Chapters 4 and 5. If the water level is above the design water level, the dike might fail and breach. The places where overtopping might occur in the river Cauca (between Canal del Sur and river Cali) for a given return period were obtained by plotting the crest height and the water levels corresponding to a given return period. The flooding scenario for a return period of 100 year was defined by comparing the height of the dike with the water level for a return period of 100 year. The locations where defined from a preliminary longitudinal profile of the dike. The OSSO-team corrected this profile after reviewing it. The locations of possible breaching of the dike were determined by the OSSO-team. The longitudinal profile of the dike at the left bank of the river Cauca shows sectors where the height of the dike is close to or lower than the water level for a return period of 100 years. Five locations were defined. In these locations the water level is higher than the dike or the free-board is less than 1 m. A free-board of 1 m is recommended by CVC. Table 4 shows the locations where overtopping might occur. The dimensions of breaching of the dike were obtained from the analyses of failures of dikes occurred in the past in Colombia [13]. Table 4 Location No. Locations where overtopping might occur Crest of the dike Abscisa [m] Water level [m] Tr 100 Tr 250 Tr K K K K K The 2D hydrodynamic model has been applied to determine the flooding characteristics. These flow characteristics and the land use maps were combined in GIS with the stage-damage functions and maximum damage costs to determine the damage costs corresponding to a flooding probability. The current yearly risk (probability x damage) has been converted to a present value by dividing by the net discount rate. A real discount rate of 8% is calculated from the interest rate of 11% minus inflation 3%. The damage will increase because of economic growth. Neglecting economic growth would lead to an NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

16 underestimation of the future risk. We have assumed a economic growth of 1% per year. This number is estimated on the basis of future expectations and is therefore uncertain. In a cost-benefit analysis also the costs of rising and reinforcing the dikes are important. The costs of relocating the families living on the dike are also taken into account in the investments. The results of the analysis are presented in Figure 4. An important feature of this calculation is that the increase in investments costs as a function of the return period is relatively small. This is because the costs of relocation the families living on the dike are the highest investment costs. This aspect leads to the consideration, that from the purely economic point of view of this method, it would be better to make a choice for the highest return period, leading to the lowest total expected costs. From a practical point of view, any choice above 500 years would seem sufficient. The background data of this calculation are presented in Annex 10. Figure 4 Results of economic optimization for the Aguablanca dike NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

17 4 IMPROVEMENT OF DIKE SAFETY, IMMEDIATE AND SHORT-TERM STRATEGY 4.1 Analysis of present conditions The objective of the assessment of the present conditions of the dike is to investigate crest levels, stability, and all human or other impacts, that may reduce the safe level of the dike. Comparing these conditions with required conditions leads to conclusions about possible strategies and necessary actions to take Dike crest level of the main dike The original design crest level for the Jarillon de Aguablanca was based on T= m. This dike protected a predominantly agricultural area between Cali and the Cauca River. The dike was constructed in an era (1950s) that T=100 could not be well calculated, but only be estimated [15]. The present crest level is presented in Figure 5 The estimation of the 1950's shows very good compliance with the now calculated T=100 in this report 3. From the analysis we have the following observations: 1. Crest level measurements show that the crest level could not be maintained all along the dike. 2. The protected area has changed from agriculture into urban area and therefore requires a higher protection level (see paragraph 4.1.3). 3. The original 1.50 m freeboard could well be reduced since the expected water levels can be calculated more accurately. Perfil Longitudinal del Jarillón del río Cauca y Nivel de agua para diferentes periodos de retorno Level [msnm] (Versión revisada con datos de campo, septiembre 20 de 2012) 956 water level T=10 water level T= water level T=100 water level T=250 water level T=500 dike crest level 954 T= ,50 m freeboard T= ,50 m freeboard T= ,50 m freeboard original design T=10 + 2, Canal Sur km m Juanchito km m Rio Cali km m > x -coordinate [km] Figure 5 Dike crest level (orange) and different water levels + freeboard (see also Annex 2) 3 With the few data the engineers had in 1958, they estimated the level corresponding to a return period of T=100 years m, to coincide approximately with a level corresponding to a return period of T=10 years m NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

18 Table 5 possible protection levels Dike lengths to be raised for distinguished flood protection levels freeboard [m] T = 10 yrs 1.50 dike length to be raised [m] almost total T = 100 yrs T = 250 yrs T = 500 yrs cm to be raised generally < 20 cm generally < 35 cm generally < 40 cm remarks with the knowledge of today's water level calculations the dike doesn't meet the originally set requirements; an extra check on the datum is required, since there is no straightforward explanation for why the Jarillón Aguablanca has fallen so far below its original standard with today's more accurate water level calculations, flood protection level of T=100 could be guaranteed with a freeboard of 0.50 m with the change of the protected area from agriculture into urban area, a higher protection level needs to be considered and should be a result of an economic analysis idem From this it is clear that the discussion about the safety level is 1. on one hand a matter of the establishment of an economical optimum return period, but 2. on the other hand a technical freeboard discussion among engineers about the reliability of the water level calculations. Accurate dike levels and accurate water levels. In the course of the assignment it turned out to be very difficult to establish the correct dike level from the available data. Level data were either outdated or, more important, taken from different periods in which the reference level (datum) had changed. CVC and OSSO have assured that the presently available dike level is correct. The hydraulic river model for water level calculations is by definition not exact, since not all riverbed data are available, nor can calibration and verification be done. Still the possibilities for establishing a more or less correct water level are way better than at the time of dike construction. A river model for the whole Cauca River should be made available. First of all, river behaviour downstream is very much affected by what happens more upstream. The acceptance of one base for transboundary decisions (between states, between municipalities depend very much on the acceptance of one base model as the true water level predictor. Still the reproduction of the original dike design (Figure 5) shows that the dike has dropped considerably below its original design value (water level T= m). This is not in line with the feeling and view of experienced local engineers. We recommend that this item will be investigated: 1. re-evaluate datum changes in the course of years 2. attribute each available measurement to the correct datum 3. describe the history of datum levels and measurements in a separate report 4. open archives to establish certainty about the really constructed dike level: T= m indeed? 5. compare the starting point T=10 (1958) and T=10 (2012) 6. investigate the possibility that the dike subsoil has consolidated so much. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

19 4.1.2 Dike conditions of Canal Sur and Rio Cali There are no records of failure of the dike along Canal Sur. Stability calculations for these dikes have also indicated that they comply with the minimum strength requirements [13]. Corporación OSSO has done field work for the dikes of the two tributaries Canal Sur and Rio Cali resulting in the longitudinal profiles presented in Annex 2. The field observations show a significant impact of human interventions along these dikes in the form of waste and rubble deposits. In addition there are nests of the ant species arriera in various locations, impacting the permeability and stability [13]. From the profiles it follows that there are some parts below the T=100 level that is defined at the point of inflow into Rio Cauca. The right embankment along Rio Cali seems everywhere, except a small part close to the Rio Cauca, well above the T=100 level as defined at the point of inflow into the Rio Cauca Water levels and river bed management Because of the intense urbanization, the river bed and flood plains condition is very much under pressure of sand mining and dumping of construction debris. Uncontrolled erosion and upward trends in water levels are a result. Of course CVC and Cali municipality are fully aware of this problem. The solution of the problem is not just a technical item, but is found in a much wider socio-economic and administrative approach Freeboard discussion In the Netherlands river dikes require a minimum freeboard of 50 cm. This freeboard allows for wave run-up, river water level model uncertainty and firm dry ground above the water level in extreme conditions for emergency measures. In the situation of the Cauca River and the Jarillón Aguablanca, wave run-up may be neglected. The width of the river is relatively small and there are no big cargo ships. The model uncertainty however needs to be regarded more in detail. For the moment we assume that model uncertainties fit well within the 0.50 m allowance for the freeboard Dike strength The crest level is the most important and direct factor for the flood level protection of Cali. However, a weak dike or weak points in the dike may result in failure, even if the water level is lower than the design water level. The dike inspection has resulted in 5 important observations. 1. Dike crossing hydraulic constructions Water and Sewer Treatment Plants and Pumping Station do not fulfil safety requirements. Especially the pumping station at the downstream side of the dike is in an alarmingly bad condition. Failure of the pumping station in its flood defence function cannot be excluded and is estimated much worse than a failure probability of 1/100 per year (T=100). Also the drinking water inlet and waste water treatment plant need upgrading. For a more elaborate description see Annex 5, Field assessment of the conditions of the Aguablanca dike. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

20 2. At high water levels some water seepage near the pumping station of Paso del Comercio has been observed, most likely due to a construction error and not to slope instability. Signs of piping effects have not been observed. 3. Ants have infested the dike and its environment (hormigas arrieras). They make their dwellings in the dike, causing cavities and weakening the dike. 4. Under the top clayey and silty layers there are some locations with a layer of liquefiable sands. Earthquake induced liquefaction may put the dike as a water retaining function out of order for long time. However, the risk of a coincidence of a major earthquake and a flood is negligible compare to the risk of the event of either a major earthquake or a major flood. Minor earthquakes in the past have not lead to liquefaction. Therefore liquefaction is not considered an issue. 5. The dike is quite densely inhabited, predominantly at the northern stretch. Housing, foundation and cellars and trees cut into essential minimum design profile. Living on a dike is almost the safest place in a flood prone area. The major problem is when housing or other human activities harm the integrity of the dike body: cut into the body itself, damage the revetment, thus reducing the water retaining capacity and creating initiation points for erosion. 4.2 Immediate and short term strategy Immediate actions Low spots Where the dike crest level of the main dike is the most important parameter in flood protection, immediate action is recommended to raise the lowest points in the Aguablanca dike that are very local: 1 km km km km km km In addition it is recommended to rehabilitate the low points of the dike of Canal Interceptor Sur, which have been identified in the longitudinal profile of Annex 2. Pumping station maintenance The condition of the pumping station is alarming. A number of the outer valves of the pumping station are not functioning. Although the pipes have inner valves, the defence against flooding should not just rely on these inner valves. During a flood, there will be unnecessary pressure inside the pipes, and increase the risk of inundation. Immediate action is required to ensure flood protection 4. 4 In a letter to Dr. M. Guerrero, the Mayor of Cali, dated December 17, 2012, EMCALI has confirmed that it is envisaged to repair the damaged valves in January NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

21 4.2.2 Short-term strategy 0 This short term strategy consists of 5 components: a. Maintaining dike level at T=100 b. River bed and floodplain maintenance c. Hydraulic constructions d. Dike slope stability e. Harmful activities from humans and ants f. Institutional issues These will be elaborated below (Institutional issues are discussed separately in Chapter 6). The short term strategy should be considered as a base strategy (maintaining the status quo is not an option). This mix of components should be implemented in a coherent way. Only maintaining the dike level at T=100 will improve safety conditions but will not be effective in the long run if components b, c,d, and e are not taken care of at the same time. a. Maintaining dike levels at T=100 For the short term strategy 0, the measures are aimed at realising the originally intended protection level of T=100. The measures respond to the findings of the dike inspection for the Aguablanca dike on 18/19 September 2012 and 2 October As regards the dikes along Canal Sur and Rio Cali, we recommend the same immediate action, i.e. to bring the levels up to the corresponding T=100 level of the Rio Cauca. Considering that the intended flood protection level of the Jarillón Aguablanca was T=100 + freeboard we recommend for the short term to rehabilitate the dike to this flood protection level. Since the protected area has changed from agricultural land into urban area, this protection level should at least be maintained. This recommendation implies raising 4300 m of the dike. In doing so, we assume that with the present statistics and calculation methods a freeboard of 0.50 m is sufficient. NB. If it would be decided to raise the dike, the reinforcement could well be combined with the longer term recommendation at little extra costs. The T= 100 does not necessarily need to be motivated with an economical analysis. Rather, the situation of Cali is such that the opposite river bank is lower and in much worse condition than the Cali side. This is for Cali a preferential situation. There is so much retention on the opposite river side that Cali is virtually safe. In this situation Cali or CVC could buy time: as long as developments upstream and/or the opposite river bank do not go so far that Q or h near Cali will rise, the Jarillón Aguablanca will provide virtually unlimited flood protection (as long it is strong enough, mind e.g. the pumping station). b. River bed and flood plain maintenance and construction debris control Enforcement of river bed maintenance needs to be improved. This is on one hand predominantly a government issue, on the other hand economical incentives and technical possibilities can help. Especially the dumping of construction debris needs to be stopped. A strong recommendation is to invest in debris crusher systems to convert waste debris into raw construction materials, ready for re-use. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

22 Figure 6 Debris crusher system c. Hydraulic constructions From the safety assessment of the Pumping Station immediate action is required. In general we recommend a situation in which the owner of the construction (EMCALI) and the owner of the dike (CVC) are equally responsible for the construction part that crosses the flood defence line. This is predominantly a governance issue to enforce this kind of collaboration, but it is also an issue of behaviour of the engineers of both organisations (see also Chapter 6). Technically we recommend EMCALI and CVC to co-operate on the ongoing projects for improvement. From a flood defence perspective a number of design issues in the rehabilitation of the structures need to be standardised: 1. construction level should be in conformity with future dike protection level; preferably far beyond the planning period (dike 50 yrs ahead, constructions more expensive to adapt 100 years ahead); 2. overall stability of the construction must fulfil stability requirement as of the dike (water levels, piping); 3. seepage screens next to and under the construction are required; 4. integrity of the construction within the flood defence line must be guaranteed, preferably the parts of the construction in the flood defence line must be stronger than parts outside the defence line; e.g. a steel pipe crossing the dike must partly be stronger in the dike: if a pipe under pressure would fail, that would be rather outside the dike than inside; 5. transition constructions from e.g. concrete to soil need to be well designed, monitored and maintained. EMCALI has projects running. From the dike perspective the hydraulic constructions need upgrading in the short term strategy. Where total rehabilitation does not fit into the life cycle economics of the structure, measures should be taken to ensure the flood protection part of the structure. Assessment and design aspects have been mentioned above. d. Dike slope stability and liquefaction The Jarillón Aguablanca has geotechnically relatively steep slopes. During the still relative low 2011 flood dike instabilities have been observed. In order to technically guarantee dike stability under design conditions the slopes should be more stable. I.e. the dike needs gentler slopes. Example geotechnical calculations show that a slope of 1:2½ to 1:3 will be required. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

23 Secondly the presence of liquefiable sands adds earthquake risk to the dike construction. Soil investigation made available shows that the omnipresent sand layer is not always liquefiable. We recommend to do density tests and test on grain size distribution and water content to localise the potential liquefaction areas. Given the Cali situation two options need to be investigated: "adding cohesion" to the liquefiable soil adjustment of the dike profile, so that deformation caused by liquefaction will not affect the water retaining integrity of the dike (PLAXIS-calculations). e. Harmful impacts from humans and ants Houses and trees cutting into essential parts of the dike profile should be either removed or the dike profile needs adaptation. We recommend the establishment and registration of minimum essential water retaining dike profile for each section. This dike profile should have a legal status by which CVC is capable of enforcing measures to maintain the minimum profile. The cavities of ant nests (hormiga arriera) need to be filled. Regular inspection should be aimed at eradication of the ants. Ant nests should be dug out as soon as observed. Shallow nest cavities can easily be repaired by digging out and applying new clay filling. Deeper nests should be filled with preferably bentonite. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

24 5 LONG-TERM APPROACH FOR FLOOD PROTECTION CALI The long term approach for flood protection depends strongly on future developments of natural causes and human activities. In this chapter developments are mentioned briefly. Essential for the developments is that they are beyond control of the dike authority as well as local and regional authorities. Yet they are an important factor that has implications for the way the flood protection in the future should be managed. 5.1 Anticipate on impact of economic and regional developments and possible climate change effects We consider scenarios as developments beyond control of the dike authority and other authorities for the region. Climate changes, effects of El Niño and La Niña, urban development population growth, economic developments are not within the immediate control of the dike authority and set boundary conditions for the dike Spatial developments Spatial development is an item that is not directly within the competence of a dike authority. This is rather the domain of the municipalities, departamentos and provinces. With respect to flood protection spatial development is an essential asset. 1. Room for natural river inundations needs to be maintained to control river water levels. Not only in the area Aguablanca, but more important upstream of Cali. 2. Where Cali is an important area to be protected, the opposite bank still has a lot of land of lower economic investment; the flood protection of Cali can well benefit from maintaining this situation: keep the protection level at the opposite bank lower than on the Cali side. In terms of spatial planning: make sure that the east side of the river can remain an emergency overflow basin. 3. Upstream developments and climate effects will in the future cause higher river water levels near Cali, requiring higher and wider dikes. The dike authority CVC should be given authority to claim and free the land adjacent to the dike. Water safety should be a leading principle in an integral approach of land use planning by the municipality and regional authorities. It is therefore an important issue related to the institutional issues Economic development Figure 7 Urbanization development NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

25 Economic and spatial developments go hand in hand. Figure 7 shows the development of 50 years. More than climatic change, land use is a driver for an increased flood protection level. In Chapter 3 we have presented a method for economical analysis to define an optimum flood protection level. Dike construction and dike reinforcement require major investments and have major impact on the environment. It should also be considered that creation of a flood protected environment will attract more investments within the protected area, thus causing a greater need for good flood protection Climate change Data that were analyzed in the recent study of the inundations in la Mojana [16], have shown a positive correlation between the occurrence of La Niña and extreme discharges in the Rio Cauca, while it has also been shown that the there is a trend in the ONI (Oceanic Niño Index), indicating an upward trend in the occurrence of La Niña. The conclusion was that the statistical characteristics of the Cauca River are changing. We conclude that besides the change of land use the occurrence of floods in the Cauca Valley is also influenced by climatic effects, the extent and magnitude of which is yet unknown. We recommend further research into the effects of the trend in the ONI on extremes of the Cauca river discharge. 5.2 Ongoing and increased need for flood protection Risk based approach for flood protection for Cali A flood is a major disaster in term of risk for loss of life, flood damage and setbacks in a long-term economic development. The Netherlands have adopted a risk based approach for flood protection. The basic philosophy is that the authorities of the flood prone area have a responsibility in "insurance of economic development, life and flood protection". For a society as a whole it is then economically attractive and feasible to invest in a sound flood protection. In the case of Cali it is therefore economically attractive to invest in river works and dikes. For the long term we therefore recommend the risk based approach. This comprises several actions: 1. acquisition of knowledge on risk based approach in flood protection 2. implementation in guidelines for dike design 3. implementation in practical operation CVC 4. thorough implementation of a risk based assessment for the Cali situation (project) Combination of flood risk and earthquake risk In an area exposed to major natural disasters the combined disaster risk is important. Cali is a disaster prone area regarding floods and earthquakes. The Colombia government has established a Construction Code requirement regarding earthquakes. A design earthquake of 7.8 on the Richter scale, resulting in 0.25 g ground accelerations is an important design factor for constructions. For Cali this design earthquake has a design return period of T = 475 years. We have the following observations: 1. living in Cali, exposure to an earthquake cannot be avoided; 2. flood risk adds to the exposure for people to disasters; 3. expected flood damage will add to the expected damage from disasters, 4. earthquake damage remains dominant NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

26 A severe earthquake may result in considerable damage to the dike, which besides all other damage to the city - would require immediate attention. Since the time of construction of the dike, no damage has been observed due to earthquake. To evaluate the risk of liquefaction due to an earthquake, we recommend more research into liquefaction prone areas. Looking at the risk of exposure to a disaster, the combination of a T=100 years flood protection with a T=475 years earth quake risk, would result in probability of disaster, which is high relative to a person s life expectancy. A person, living 80 years in a flood and earthquake prone area runs the risk of 68% to be hit by at least one of the two. Where the earthquake can hardly be avoided once living there, reduction of this exposure is well possible by increasing the flood level protection. For instance, the combination of a T=500 year flood risk with a T=475 year earth quake risk, would result in a probability of 28% of being hit by at least one of the two disasters in a period of 80 years. From the damage point of view the earthquake risk is quite high. Considering that a dike breach would not result in very high inundation depths in Cali, damage is severe, but would still be limited in comparison with a major earthquake. Economic optimisation will therefore decide on the optimum flood protection level. In Chapter 3 we have shown that, having done the initial investment for dike improvement (predominantly resettlement), a high flood protection level is economically attractive. The small differences in cm between the low frequency water levels (T=100 to T =2000 and higher) demand little extra cost for great value in avoided damage. 5.3 Strategies for maintaining and improving flood protection From the above considerations two main strategies for the Jarillón Aguablanca can be formulated. 1. The first strategy aims at "keeping the pressure on the dike low". Mitigation of rising river water levels is the guideline for this strategy. This involves sound spatial planning. 2. The second strategy assumes that spatial development can hardly be controlled when it comes to flood protection. Retention capacity more upstream and opposite to Cali will gradually disappear for other developments, forcing Cali to rely more and more on the flood protection of the Jarillón Aguablanca Flood protection level Based on the scenarios, the right margin of the Cauca River will probably become economically more valuable than at present. It is therefore expected that the right margin will also be better protected against floods. Socio-economic developments more upstream will lead to the construction of more upstream flood protection works. As a result the flood protection level of Cali that is provided by the dike at its present level will decrease. After all, reduction of room for inundation of river water will decrease the upstream retention capacity and therefore have an upward trend in river water levels at Cali. This goes along with an increased need for flood protection: economic development and growth of population and properties in Cali will demand safety. From the economic analysis it is clear that an economic optimum can be found in raising the protection level of the Jarillón Aguablanca to at least T=500. Higher protection levels can be acquired at little extra costs. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

27 5.3.2 Strategy 1: Controlled retention upstream of Cali and on east bank Based on the present behaviour of the river water levels there is still sufficient room for retention of river water upstream of Cali and on the right bank. A good 2D river model would need to be developed to confirm this. In the calculation of river water levels at lower frequencies (T=250, 500, 2000 etc) the right margin has been modelled as a infinitely high dike and a statistically extrapolated inflow from upstream. Reality will be that Jarillón Aguablanca is the strongest point and that at lower frequencies, higher discharges water levels will show little rise because of inundations elsewhere. Water authorities in the States Valle de Cauca and Cauca might be able to maintain the upstream river retention capacity, although experience shows that spatial development is rather difficult to control. This strategy therefore comprises: 1. upgrading of the Jarillón Aguablanca according to strategy 0 2. further upgrading of the Jarillón Aguablanca to a higher protection level T=500 up to T=2000; this further upgrading needs to be done along with strategy 0 to avoid double initiation costs; it needs to be based on a good new 2D river model; relocation of all housing may even be avoided; 3. CVC and their upstream colleagues will need to co-operate intensively, the same holds for the State authorities 4. Enforcement of spatial management and assessment of spatial developments on consistency with the long-term flood approach needs to be implemented. Special areas now being part of the river retention area already need to be dedicated for controlled flooding at large scale. Figure 8 The three strategies shown in the flood-frequency graph Strategy 2: Total reliance on Jarillón Aguablanca The assumption for strategy 2 is that spatial management and maintaining retention areas available for flood protection fails. As a result Cali will face higher extreme water levels. Cali will need to raise the Jarillón Aguablanca to maintain and raise its flood protection level. Also in this strategy Cali's flood protection level depends on upstream developments and on its own way of operating the right margin of the Rio Cauca at Cali. This strategy comprises: NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

28 1. upgrading of the Jarillón Aguablanca according to strategy 0 2. further upgrading of the Jarillón Aguablanca to a higher protection level of T=500 up to T= resettlement of all houses on the dike and in the berm of the dike cannot be avoided; 4. considerable enlargement (widening) of the dike needs to be accounted for Choice of strategy The presented strategies were developed with an open mind not wanting to limit ourselves a priori, and without looking at financial or institutional implications. Taking a closer and more realistic look at the possibilities, we recommend the choice for strategy 2. This strategy is included in the action plan. We recommend a safety level with a return period of T=500 years. The arguments are the following: 1. Spatial development is a process which is very difficult to control and includes too many parties. The strategy which includes use of designated retention areas may therefore prove impossible to realize or be unreliable in the future. 2. The extra costs involved in going from a protection level with T=100 year to T=500 years are marginal as compared to the overall costs NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

29 6 GOVERNANCE AND WATER AUTHORITY The organisational framework for river and dike management for the Cauca River, its tributaries and the dikes, is scattered. In 1993 river and dike management were divided along political and administrative boundaries. The Corporación Autónoma Regional del Valle del Cauca (CVC) was split in terms of both geographical authority and content wise. Cauca was separated from Valle del Cauca and environmental was separated from technical contents. This had very adverse effects on dike maintenance and management, resulting in deterioration of the dike. Part of this deterioration has been caused by illegal housing and other illegal activities on and around the dike. Officially CVC is owner of the dike body 5 and should still have responsibilities for maintenance and management. In practice this is not the case and at the same time CVC does not have sufficient technical staff to fulfil such a task. However, within the Colombian setting of authorities, CVC comes closest to being a regional authority involved in water management, although its tasks related to management of the dike are not clearly described. Authorities like EMCALI are responsible for certain constructions in the dike body, such as the main pumping station, and the drinking water intake. However, there is hardly any consultation with CVC about their activities for renovation and status of the construction works, whereas these constructions are part of the defence of the dike. It follows that there is no protocol for dike management and maintenance because obviously there is no organization that holds complete responsibility. We recommend that maintenance and control of the Aguablanca dike comes under one authority only that has the legal mandate to do so, respected by all other organisations. This authority should have the legal right to inspect, monitor, evaluate plans and grant permissions of any construction that is part of the dike and thus part of the defence against inundations. There is more to this issue than management of the dike near Cali alone. It is about management of the whole Cauca River from the Salvajina Dam up to and beyond Cali that should be managed by one authority, and regulated by law. We recommend a dialogue between the parties concerned, led by the mayor of Cali, or by the central government, to resolve this issue. As an example of a water authority framework Annex 8 presents an introduction of the Dutch organization of regional water authorities. 5 At the time of writing the draft report in November, this still appeared to be the case, i.e. until November 7, 2012; on December 6, 2012, we were informed that CVC has signed of its ownership to the municipality, but we have not seen the documents to confirm this. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

30 7 REFERENCES [1] Caracterización y modelación matemática del Río Cauca - PMC FASE III; Evaluación y optimización de la regla de operación del embalse de Salvajina, VOLUMEN XVI, Universidad del Valle, Facultad de Ingeniería, Escuela de Ingeniería de Recursos Naturales y del Ambiente, Santiago de Cali, mayo de [2] Modelación matemática del sistema Rio Cauca-Humedales; Universidad del Valle, Facultad de Ingeniería, Escuela de Ingeniería de Recursos Naturales y del Ambiente, Grupo Hidráulica Fluvial y Marítima HIDROMAR, Santiago de Cali, Agosto de 2009; Convenio Interadministrativo 144 de 2008 entre la CVC y la Universidad del Valle. [3] Lit 1. Modelación de amenaza por inundaciones en la ciudad de Cali por el Río Cauca y tributarios, incluye mapa de amenazas, batimetría y topografía en ambos costados. Informe final. Versión 01. Hidro-Occidente S.A. [4] Lit. 2. Modelación matemática del sistema Río Cauca Humedades. Volumen 1. Universidad del Valle. Facultad de Ingeniería. Escuela de Ingeniería de Recursos Naturales y del Ambiente. Octubre [5] Lit. 3. Proyecto Corredor del Río Cauca (CVC). [6] Lit. 4. Best Practise Guidelines for Flood Risk Management. The Flood Management and Mitigation Programme, Component 2: Structural Measures & Flood Proofing in the Lower Mekon Basin. Deltares, Royal Haskoning and UNESCO-IHE. Draft final report. May [7] Lit. 5. Penning-Rowsell, Chatterton, J.B. (1977). The benefits of flood alleviation a manual of assessment techniques, Saxon House, ISBN [8] Lit. 6. Dutta, D., Herath S., Musiake K. (2003). A mathematical flood loss estimation, Journal of Hydrology, 277: [9] Lit. 7. Kok M., Huizinga H.J., Vrouwenvelder A.C.W.M., Van den Braak W.E.W. (2005). Standaardmethode2005 schade en slachtoffers als gevolg van overstromingen, HKV report PR [10] Lit 8. Jonkman S.N., Bockarjova M., Kok M., Bernardini P. (2008) Integrated Hydrodynamic and Economic Modelling of Flood Damage in the Netherlands, Ecological Economics 66, pp [11] Lit. 9. Metodología de Modelación Probabilista de Riesgos Naturales. Informe Técnico ERN-CAPRA- T1-5. Vulnerabilidad de edificaciones e infraestructura. ERN. Consorcio Evaluación de Riesgos Naturales América Latina. Consultores en Riesgos y Desastres. Tomo I. [12] Rijkswaterstaat Standaardmethode2004. Schade en Slachtoffers als gevolg van overstromingen. Kok M., Huizinga H.J., Vrouwenvelder A.C.W.M., Barendregt A. DWW [13] Informe de avance n 2. Contrato de consultoría n 101 de 2012 celebrado entre el fondo adaptación y corporación observatorio sismológico del sur occidente contrato de consultoría n 101 de 2012 NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

31 celebrado entre el Fondo Adaptación y Corporación Observatorio Sismológico del Sur Occidente; Corporación OSSO, Cali, octubre 29 de 2012 [14] Water governance, The Dutch regional water authority model; Unie van Waterschappen, 2011 [15] Aguablanca Project 18 November 1958, Hadjikoulas, Kirpich, Corporación Autonoma Regional del Cauca [16] Flood risk management for La Mojana; Deltares, Royal HaskoningDHV, HKV; august 2012; Agency NL NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

32 ABBREVIATIONS Table 6 List of abbreviations Abbreviation Explanation CVC Corporación Autónoma Regional del Valle del Cauca DAGMA Departamento Administrativo de Gestión del Medio Ambiente (del Municipio de Cali) EMCALI Empresas Municipales de Cali EPSA Empresa de energía del Pacífico S.A. ONI Oceanic Niño Index NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

33 8 COLOPHON NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia LW-AF Client Project File Length of report Author Contributions Internal check : NL Agency : Aguablanca Dike along the Cauca River, Cali, Colombia : BB2984 : 31 pages : Hans Leenen : Marcella Busnelli, Michel Tonneijck, Steven Sjenitzer, Joop de Bijjl : Erik Arnold Project Manager : Martijn van Elswijk Project Director : Date : 31 January 2013 Name/Initials : NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia 31 January 2013, version final LW-AF

34 HaskoningDHV B.V. Laan 1914 no EX Amersfoort P.O. Box BC Amersfoort The Netherlands T F

35 ANNEX 1 Hydrology NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 1 LW-AF

36 Table 7 Juanchito hydrometric station: maximum annual level and discharge Year Maximum discharge (m3/s) Maximum level (m local reference) Reference level (m.s.l) Actual level (m.s.k) , , , , NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 1 LW-AF

37 Year Maximum discharge (m3/s) Maximum level (m local reference) Reference level (m.s.l) Actual level (m.s.k) , , , [m3/s] 1400 Current water level - discharge relation (from table and fitted equation of third order) y = 0.008x x x R 2 = Table Formula > water level [m local reference] Table 8 Current water level discharge relation from table and fitted equation of third order NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 1 LW-AF

38 Table 9 Juanchito: Current water level discharge relation (provided by CVC, ) H Q NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 1 LW-AF

39 H Q NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 1 LW-AF

40 30 Moment Ratio Diagram Gumbel Weibull LP3 Observed LN2 Normal Gamma Logistic 25 Ck (Kurtosis coefficient) Cs (Skewness coefficient) Figure 9 Moment-ratio diagram of observed extremes and theoretical probability distributions Note: For a given distribution, conventional moments can be expressed as functions of the parameters of the distributions. It follows that the higher order moments can be expressed as functions of the lower order moments. Figure 9 presents the moment-ratio diagram of the Skewness coefficient en the Kurtosis coefficient for a number of well known distributions, as well as for the observed values of the maxima of the Rio Cauca at Juanchito (the blue dot). For some of the distribution functions the ratio follows a curve, for others it is a distinct point in the graph. This merely is a characteristic of the particular distribution. The figure shows that the Skewness-Kurtosis ratio for the observed values practically coincides with the theoretical value for the LP3 distribution. Furthermore it shows that the Skewness-Kurtosis ratio for the Gumbel distribution is far off the ratio of the observed values. The conclusion is that the momentcharacteristics of the observed values correspond much better with the LP3 distribution than with the Gumbel distribution. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 1 LW-AF

41 ANNEX 2 Longitudinal dike profiles and hydrodynamic modelling results NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 2 LW-AF

42 Crest level of Jarillón Agua Blanca and calculated water levels + required freeboard Perfil Longitudinal del Jarillón del río Cauca y Nivel de agua para diferentes periodos de retorno (Versión revisada con datos de campo, septiembre 20 de 2012) Level [msnm] 956 water level T=10 water level T= water level T=100 water level T=250 water level T=500 dike crest level 954 T= ,50 m freeboard T= ,50 m freeboard T= ,50 m freeboard original design T=10 + 2, Canal Sur km m Juanchito km m Rio Cali km m > x -coordinate [km]

43

44

45 Figure 10 Inundation modelling Location of breaching Scenarios return period 1/100 years Location No. 6 Location No. 5 Location No. 4 Location No. 3 Location No. 2 Location No. 1 Breaching in all the locations Location No.1 NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 2 LW-AF

46 Location No. 2 Location No. 3 NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 2 LW-AF

47 Location No. 4 Location No. 5 Location No. 6 NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 2 LW-AF

48 ANNEX 3 Hydrodynamic modelling, methodology NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 3 LW-AF

49 Calibration of the model The model was recalibrated to fit the water level at the station Juanchito for the different return periods. The roughness coefficient in the main channel was tuned. Furthermore the bathymetry at the right margin, where the data is less accurate, was adjusted. The water levels in the station Juanchito for the different return periods were reproduced with an error of approximately 10 cm. Besides the water levels at a location upstream of the station Juanchito were compared with the values obtained from the hydrological analysis of the data of the station Juanchito and the translation to locations upstream and downstream by applying the water slopes calculated with a 1D-model [4]. The maximum difference calculated is about 10 cm. Modelling of the flooding scenario s In order to simulate the flooding scenario s the boundary conditions upstream and downstream were defined. Upstream the flood hydrograph was defined on the basis of the measured hydrograph in For every return period a flood hydrograph is obtained. These flood hydrographs are shown in Figure 11. Downstream the water levels were obtained from the Q-h relation in Juanchito and after that they were extrapolated to the location downstream. These water levels are shown in Figure 12. The locations of overtopping were modelled as a change in the bathymetry. To our knowledge it is not possible to include in the CCHE2D model constructions such as weirs (sub-grid modelling of constructions). Due to that fact, the grid has been refined to reproduce the height of the dike. Figure 11 Upstream boundary condition NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 3 LW-AF

50 Figure 12 Downstream boundary condition Recommendations There are uncertainties in the numerical modelling but also in the data. Monitoring of water levels and discharges should be continued. We advise to include more measurement locations, upstream and downstream station Juanchito. Furthermore it is important to determine for which levels flooding have occurred upstream Juanchito because this flooding has influence on the water levels and discharges in station Juanchito. The following recommendations are given concerning the hydrodynamic model in order to improve the accuracy of the modelling results: 1. Update the digital elevation data to improve the model results. The bathymetry to the right margin should be included. Furthermore mainly due to human actions the bathymetry of the main channel and floodplains might have changed and needs to be updated. 2. Develop an integrated hydrodynamic model of the river Cauca starting at Salvajina reservoir. In this model the overtopping and flooding should be included. The model should be calibrated in order to reproduce the last flooding events for instance by comparing the inundated area with aerial photographs. These simulations will give more insight in the discharges through the river Cauca since also overtopping and flooding would be included. We understand that this model will be constructed in another project [5]. We advise the local team to participate in this study so that the experience gained in the modelling of the river Cauca along the city of Cali can be shared, in order to improve the modelling system. 3. In choosing the numerical model, we recommend that constructions such as weirs and roads be accurate schematized. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 3 LW-AF

51 Considerations concerning fluvial morphodynamics During the study and conversations with the local team some morphodynamic issues arose. Amongst these issues we list the following: 1. Local erosion: for instance in the location Nuevo Amanecer erosion in the left margin has occurred probably as result of a bank protection carried out at the right margin. 2. Bank erosion related to natural meandering of the river may affect the stability of the dikes. 3. Dredging activities (illegal) are carried out in this part of the river Cauca. These dredging activities may lead to erosion of the river bed. However there is no clear indication of large scale erosion of sedimentation of the river Cauca. 4. The construction of the Salvajina reservoir will have had an influence on the morphological developments of the river Cauca due to the changes in the discharges and sediment loads. 5. There are indications of changes in discharges and sediment load in the Canal Interceptor del Sur due to human activities such as deforestation that may also have influence on the morphological developments of the river Cauca. 6. The bed in some parts consists of a hard soil deposit (mixture of clay, silt and sand), which is in Cali called Caliche. Due to this soil the bed level has remained rather stable. Between this hard soil, there is sand that can be eroded. Local erosion occurs in those sections. We recommend that the fluvial morphodynamics of the river Cauca be studied in order to have a better understanding of its morphodynamics and the influence of the human activities on the morphological developments. We have the following recommendations: 1. Monitoring the bed evolution of longitudinal profiles of the main river. Is there a trend (erosion, sedimentation of stable) in the bed level? 2. Monitoring bank erosion since it might influence the stability of the dikes and banks. 3. Obtain information over the soil and subsoil of the main river. Critical locations are where a sand layer in the subsoil may be cut by ongoing erosion. Such locations ask for more extensive monitoring. 4. Obtain information of the dredging activities: dredging site, dredged volumes, properties of the dredged material. 5. Prepare a plan for managing the bed levels where also dredging activities are carried out in a control manner, by defining where it is possible to dredge and how much. Geotechnical stability of dikes and banks needs to be guaranteed, and therefore the riverbed should not incise too much. Such demands to the riverbed require that the river manager needs to assess the development of the bed and to intervene in the river system if necessary. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 3 LW-AF

52 ANNEX 4 Flood risk management methodology NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 4 LW-AF

53 Concepts The word risk refers in general to the probability of loss or harm. In the context of flood risk management it denotes the combination of the probability of a flood and its consequences. In this context also the terms hazard and vulnerability are often used. Hazard refers to the source of danger, i.e. the probability of flooding. Vulnerability relates to potential consequences in case of an event [6]. Integrated flood risk management is an approach to identify, analyze, evaluate, control and manage the flood risks in a given system. Figure 13 presents a general scheme for flood risk management. The following steps are defined: Definition of the system, the analyzed hazards and the scope of the analysis. A quantitative analysis where the probabilities and consequences are assessed and combined/displayed into a risk number, a graph or a flood risk map. Risk evaluation: with the results of the former analysis the risk is evaluated. In this phase the decision is made whether the risk is acceptable or not. Risk reduction and control: dependent on the outcome of the risk evaluation, measures can be taken in order to reduce the risk. Measures could concern structural and non-structural measures. It should also be determined how the risks can be controlled and managed, for example by monitoring, inspection or maintenance. The scheme focuses on minimization of flood risks to an acceptable level. The approach could also be used to assess the overall hydrological performance of the system (e.g. minimization of drought, maximization of water quality and ecological quality). Then the approach will focus on multiple objectives: not only to minimize the risk, but also to maximize the performance. Figure 13 General scheme for flood risk management NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 4 LW-AF

54 Approach for economic damage assessment Scope of the analysis The scope and level of detail of the damage evaluation has been defined on the basis of the spatial scale of the study and the availability of data. Due to the fact that very precise methods require more effort (i.e. time and money) than less detailed approaches and that the resource are usually limited, the most precise methods are often restricted to small areas under investigation, while studies with a research area of regional or even national size mostly have to rely on less detailed methods. The area of the study is the flood area of the city of Cali, at the left margin of the river Cauca between Canal Interceptor del Sur and the river Cali. At the right margin of the river Cauca lays the city of Calendaria, where there is no bathymetric information available for the study. In this study we focus on the priced direct damages. This category of damage constitutes the largest part of the total damage. For example in the standardized damage method that is used in the Netherland the following main damage categories are considered: land use, infrastructure, households, companies and other. Within each main categories, sub-categories are distinguished (e.g. agriculture, urban area, or recreation within the main category land-use). Direct damage assessment Methods for the estimation of the direct economic damage to objects, such as structures, houses are well established, and the use of so-called damage functions is widespread ([7], [8], [9], [10]). The procedure for the estimation of direct physical damages [12] is illustrated in Figure 13. The procedure comprises three main elements: - Determination of flood characteristics - Assembling information on land use data and maximum damage amounts - Application of stage-damage functions. We describe these elements in more detail below. Determination of flood characteristics Flooding patterns are in general simulated with a two dimensional hydrodynamic model. The existent 2Dmodel of the University of Mississippi of the river Cauca between the Canal Interceptor Sur and the river Cali was applied for this study. This model was recalibrated since the statistics of discharges and water levels was updated in this study. The water levels in the station Juanchito for the different return periods were reproduced with an error of less than 10 cm. The model runs were carried out by Angela Cabal of the corporation OSSO (local partners in Colombia). A complete description of the model is given in [3]. The model has some limitations but there are also restrictions on the available data mainly in the flooding area. For instance there is not information of the bathymetric on the right margin of the river Cauca and therefore the inundation of the city Candelaria is not included. In this study we applied the existent 2D-model and we made recommendations for a more accurate modelling system and for the required data collection for future studies. The hydrodynamic model provides insight in flood characteristics, such as water depth, flow velocity and the rate at which the water rises. All these characteristics can be depicted on a map. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 4 LW-AF

55 Flood risk assessment Definition In the risk assessment the results of hazard and damage assessments are combined. Flood risk is generally defined as follows: Risk = Probability x Damage For example, if an area has a probability of flooding of 1% per year (or 1/100 per year) and the damage is 100 million COP, the risk equals 1 million COP per year. As this risk number reflects the average expected economic damage per year, it is also referred to as yearly expected economic damage. The flood scenarios can be defined depending on their return period, i.e. the average recurrence interval between the occurrence of two floods with a certain flood level and corresponding damage value. It is also possible to determine the probability of exceedance of an event with certain damage. That is the probability (per year) that a certain damage value will be exceeded so that: Probability of exceedance = 1 / return period This means that the event a 100 year return period has a probability of exceedance of 1/100 per year. Economic optimization The economic optimization approach is applicable to determine an optimal level of protection when investments in the protection and the risk are dependent on the level of protection. This is for example the case for flood prone areas that are protected by dikes. In that case the decision problem becomes the choice of the height of the dikes and thus the choice for the protection level that de dikes provide. According to the method of economic optimization, the total costs in a system are determined by the sum of the expenditure for a safer system and the expected value of the economic damage. In this economic optimization the incremental investments in more safety are balanced with the reduction of the risk. The investments consist of the costs to strengthen and raise the dikes. In a simple approach it is assumed that flooding could only occur due to overtopping of the flood defences. Thereby each dike height corresponds to a certain probability of flooding (the higher the dikes the smaller the probability of flooding) and an associated damage. By summing the costs and the expected damage or risk, the total costs are obtained as a function of the safety level. A point can be determined where the total costs are minimal, the so-called optimum (Figure 14). In the optimum the corresponding dike height is known. Because the statistics of the water levels are also known, the corresponding protection level in terms of a probability can be defined. The economic optimization approach was applied to flood protection systems by the Delta Committee in the Netherlands. This Committee investigated possibilities for new safety standards after a major flooding caused enormous damage in the Netherlands in Eventually these results have been used to derive safety standards for flood defences in the Netherland. For coastal areas protection has been chosen with exceedance probabilities of 1/4,000 per year and 1/10,000 per year. For the Dutch river areas the safety standards were set at 1/1,250 per year and 1/2,000 per year. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 4 LW-AF

56 Figure 14 Principle of economic optimization NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 4 LW-AF

57 ANNEX 5 Field assessment of the conditions of the Aguablanca dike NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 5 LW-AF

58 Introduction Three dike visits were made. On Wednesday 19 th of September a boat visit was made followed by an dike visit by car on Thursday 20 th of September. On Tuesday 2 nd of October a final visit has been made to the pumping station Paso del Comercio and the PTAR (drinking water treatment plant). The objective of these visits was to have a visual inspection of the physical condition in general and of the envisaged problems at two structures in particular. As a general observation we conclude that the dike is deteriorated by lack of maintenance, sewerage systems and roads that cross the dike, and ant invasions and tree roots. Later on the constructions through the dike were studied and geotechnical calculations done. The inspection is documented by photos and technical information. The main goal of the inspection was to locate the weakest spots and to make an inventory of the most needed and effective short term measures. Boat visit (Wednesday 19th of September) and dike visit (Thursday 20th of September) The inspections of the dike resulted in 8 points of attention 1. Debris dumping There has been a lot of debris dumping on riverside of the dike. This dumping of debris becomes an obstacle for the river during a flood and will raise the water level. It is therefore important to stop illegal dumping of debris. Cali acknowledges the problem and has already started with the removal of the debris, but the problem continues. It is recommended to search for alternative dumpingsites. Debris does not have to be a waste material, but can be used as base material. Therefore a debris crusher instalation is needed. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 5 LW-AF

59 2. Crest level Historic information by Hidro-Occidente (Guillermo Regalado) provides the following: When the Aguablanca dike was designed in 1957, the consultants only had 10 years of data available. With these data they estimated the maximum of those years to have a return period of 10 years. They also estimated that with a freeboard of 1.0 m, the crown of the dike could manage a water level corresponding with a return period of 100 years. An important issue, confirmed by Ingeniero Jorge Llanos, who participated in the studies, is that during construction of the dike, another 1.5 m was added to the crown level, corresponding with a return period of 100 years. It thus follows that the dike was constructed with a freeboard of 2.50 m above the level of a return period of 10 years. (Original communication by Guillermo Regalado: Los consultores, con los pocos datos existentes ( ) estimaron que la creciente de los años 50 tenía un Tr de 1 en 10 años. Estimaron también que si se adoptaba un borde libre de 1.0 m el nivel del agua, coincidiendo con el nivel de la corona o cresta del dique, podría manejar una creciente de Tr= 1 en 100 años. Algo muy importante, confirmado con el ingeniero Jorge Llanos que estuvo en el proceso de estudios, es que para construcción se incrementó en 1.5 m el nivel del dique con relación al nivel del agua adoptado para una creciente de 1 en 100 años (ver punto C, página 4 del informe de los consultores Kirpich y Hadjiluokas). Ese incremento se realizó; es decir que con relación a los niveles de agua de 1 en 10 años (creciente de los años 50), la corona o cresta del dique quedó construida con un borde libre (freeboard) de 2.50 m) Nivel_TR10 Nivel_TR25 Nivel_TR100 Nivel_TR250 Nivel_TR500 Dike level Perfil Longitudinal del Jarillón del río Cauca y Nivel de agua para diferentes periodos de retorno Level [msnm] (Versión revisada con datos de campo, septiembre 20 de 2012) Canal Sur km m Juanchito km m Rio Cali km m > x -coordinate [km] Figure 15 Longitudinal profile of the Aguablanca dike based on direct field monitoring, and water levels corresponding with different return periods NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 5 LW-AF

60 3. Hydraulic constructions During the dike inspection it was noticed that a few construction show damage and some other constructions can potentially cause damage in the future. The constructions are mostly owned by corporations or parties that are not primary responsible for the safety of the dike. The construction which shows the most damage is the pumping station Paso del Comercio. An extra visit was made at this construction on Tuesday 2 nd of October. 4. Land side slope is steep The slope of the dike on the land side is mostly between 1:1.5 (66%) and 1:2 (50%). Considering safety requirements of T = 100 or better the slope is considered to be quite steep. It is recommended to create a gentler slope on the land side of the dike. For an optimum slope, geotechnical calculations have to be made. In the Netherlands often a minimum slope of 1:3 (33%) is used. This has a lot of positive effects: maintenance of a 1:3 slope is better, damage of people, animals is less probable a gentle slope will better resist overflowing or overtopping water (erosion control) where a thin cohesive top layer and short distance to the river coincide, land side slope stability and piping is more of a problem. A more gentle slope will accomplish more safety on these failure mechanisms earthquake induced liquefaction will yield less damage for gentler slopes 5. Animal activity During the dike inspection it has been noticed that there is a lot of activity of ants. These ants cause a lot of damage by digging holes in the dike. These holes can cause water transportation through the dike followed by erosion of the dike. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 5 LW-AF

61 It is recommended to exterminate ant activity as much as possible. Therefore the following activities are needed: Implement consequent monitoring of ant activity and anthills (e.g. every month) maximum intervention level of displaced soil, e.g. 50 to 100 liters filling of anthill cavities, preference bentonite consequent killing of ants 6. Earthquake and flood It is not probable that an earthquake and a flood coincide. However, one may take into account that a flood might come within a year after a major earthquake. Considering that a major earthquake might induce liquefaction, resulting in serious dike deformation, it is recommended to identify potential liquefiable areas and limit the problem. 7. Housing and trees on the dike It has been noticed that housing and trees cut into essential minimum design profile. This makes the dike more vulnerable for stability and piping problems. NL Agency/Aguablanca Dike along the Cauca River, Cali, Colombia appendix 5 LW-AF