San Diego County: Assessment of water resources, green infrastructure, and utility rates

Transcription

1 Spring 2014 San Diego County: Assessment of water resources, green infrastructure, and utility rates Authors: Christine (Hui) Wen, Mary Williams, Christopher Economides, and Nelson Dove Advisors: Naresh Devineni, Tess Russo, and Upmanu Lall COLUMBIA UNIVERSITY WATER CENTER

2 Table of Contents Summary Water Resources Assessment Water Consumption Historic Groundwater Levels Historic Precipitation Drought Vulnerability Green Infrastructure Utility Rates References

3 Summary This report provides a look at water resources in San Diego County. We specifically address five subject areas: (1) Water consumption, (2) Groundwater elevation levels, (3) Vulnerability to drought, (4) Green infrastructure, and (5) Utility rates. Each of these topics is assessed for San Diego County using data ranging between 1949 and 2013, depending on the topic. The City of San Diego is the 8 th largest city in the United States and the second largest city in California. Today with a population of 1.3 million, the city has claimed the title of America s Finest City. The following report will paint a unique picture of the city and county from several key perspectives and illustrate San Diego s relationship to water. A majority of water consumed in San Diego County is imported from northern California and other states. Local groundwater levels have been declining, resulting in salt water intrusion even though much of the water supplied is imported. Water stress indices developed in this paper confirm the dependence on imported water to growing water demands given insufficient local supply. San Diego has plentiful access to saline surface water which the county uses for thermoelectric purposes. Over 2000 wells in San Diego County have records between 1949 and 2009, however only 68 of them have data that span at least 20 years and can be used for time series analysis. Wells are primarily located in clusters throughout the outer rims of the county. There are no wells in the center where rivers and creeks are densest. The shallower wells (70 to 150 ft. deep) in the northwestern part of the county generally showed no significant trend between 1949 to 1978, after which they are not monitored. The deeper wells (>300 ft.) located in the arid northeast saw significant declines over the study period. San Diego has relatively low annual precipitation. However, due to a lack of treatment facilities for stormwater runoff, beach closings due to contaminated runoff occur. The department of Transportation and Storm Water is leading local efforts to improve best management practices related to storm water retention and treatment. Their Think Blue program is focused on outreach, working with developers and contractors, and has already constructed several pilot projects. Residential water rates for customers in San Diego County have increased significantly over the past decade while the total water sales made by the utilities have decreased. This places the San Diego Water Authority in a delicate situation where they need to develop ways to accurately price water services to recover increasing costs. For San Diego, this pricing is dependent on many external factors including transportation of water into the county from other parts of California. 2

4 The report will address the following research questions: How much water is consumed in San Diego County? How much comes from surface water and how much from groundwater? How has this distribution changed from 1985 to 2005? Are groundwater resources changing over time? Are changes uniform across the county? What is the county s vulnerability to drought? Does the city have a well-defined agenda for implementing Green Infrastructure as a stormwater management tool? If so, how effective is their Green Infrastructure Program? Is there one or multiple departments that oversee the management, implementation and tracking of Green Infrastructure Projects? How have utility rates changed in the past 10 years? How does the change in rates relate to how much water is being sold by the utilities? What are some actions that are being implemented reduce the rate of increase in residential water costs? 3

5 1. Water Resources Assessment 1.1 Water Consumption San Diego County largely relies on water imports to supply the water needs of its 3.2 million people, including the City of San Diego. Between 85%-90% of the drinking water in San Diego is imported via the California Aqueduct and the Colorado River Aqueduct. The remaining 10%-15% of drinking water comes from local surface water reservoirs. 1 To further augment water supply, the San Diego Water Authority is planning the construction of the largest desalination plant in the Western Hemisphere. This plant is set to open in 2016, and will greatly reduce the stress on local fresh water sources. Other forms of supply generation and demand management in San Diego include water recycling programs and water conservation policies. 2 Water Consumption and Diversion (MGal/d) Figure 1. Total local water resource use in million gallons per day classified by surface water, groundwater, fresh and saline. Fresh groundwater and surface water are consumptive uses, while surface saline water is diverted for thermoelectric power generation rather than consumed. Total fresh water withdrawals have increased overall since 1985, however the highest consumption was seen in 2000, not the most recent recorded year (2005) (Figure 1). Fresh groundwater use ranges between 7 to 17% of total local fresh water use, with the largest percent and quantity of groundwater withdrawn in the most recent record, 2005 (Figure 2). Given its dependence on imported surface water, San Diego County is vulnerable to the effects of climate change and variability in the source regions of the California and Colorado River Aqueducts. 4

6 Figure 2. Total fresh groundwater and fresh surface water use in San Diego County (Source USGS). Fresh water is used primarily for public supply and irrigation (Figure 3). The amount of water withdrawn for public supply has remained relatively stable compared to the amount of water withdrawn for irrigation. Saline surface water is the most utilized local water type. More than 99% of saline surface water is used for thermoelectric power generation. Figure 3. Total fresh water used for public supply (dark blue) and irrigation (light blue) in San Diego County. 1.2 Historic Groundwater Levels This section details groundwater level changes in San Diego County between 1949 and

7 Figure 4. Depths of all wells that have been measured at least once in San Diego County. Depth is shown with a color gradient ranging from shallow (light blue) to deep (dark blue). All groundwater level data was obtained from the US Geological Survey (USGS). There are 42,150 well sites in California, with 2,717 in San Diego County (Figure 4). Of these, 2,606 wells have records between years 1949 and 2009, inclusive. Many have only been measured only once or twice and therefore provide no long-term trend information. To preclude wells with short records unlikely to span multiple years, we set a minimum requirement of 30 observations. This reduces our study sample to 280 wells, all having records between 1949 and 2009 and 30 minimum observations overall, which provide us with a total of 39,707 individual water table measurements (Figure 5). Figure 5. Locations of the 280 wells with minimum 30 observations shown in red. Other well locations shown in white. 6

8 A majority of the wells have been measured fewer than 100 times. Measurements were rarely recorded at regular intervals, with the total number of measurements taken each year varies by site (with very few exceptions). For example, there are cases where a well may have been measured more than 30 times overall, but all of these take place within one year. This temporal frequency is useful for seasonal analysis, but does not provide information over multiple years, which is the present interest. To account for this, we apply a second filter which requires groundwater elevation records in at least 20 years (non-consecutive). The second filter reduces the dataset size for San Diego County to 68 wells. Using the subset of wells with records in more than 20 years, we assess the long-term trend in groundwater elevation (Figure 6). Many of the historical records end in the mid-1980s, which is likely due to Federal budget cuts to the USGS 3. The longer records suggest a general decline in groundwater elevation for most of the wells beginning in the mid-1980s and lasting to the present, especially for the deeper wells. Figure 6. Depth to groundwater for wells with at least 20 years of records. To characterize the groundwater elevation behavior before 1987, we use a k-means cluster analysis on well records with continuous temporal coverage. There are 17 wells that have continuous record between 1950 and We used k=4 for the cluster analysis and will address results of two of the clusters. The two clusters shown in Figure 7 include seven wells with depths ranging from 100 to 150 ft. The wells in both clusters are located in the northwest area of San Diego County, near the Pacific coast. Cluster A has a general upward trend; these five wells lie in the same aquifer and are located close to one another (Figure 7A). Cluster B has two wells with nearly identical behaviors (Figure 7B). The remaining clusters do not have the same coherence. 7

9 A B Figure 7. Groundwater elevations for two of the clusters for 17 wells with continuous records between 1950 and (A) Cluster A shows a general increase in groundwater elevation. (B) Cluster B shows very similar trends for two wells ranging between depths of 40 to 10 ft. below ground surface. Figure 8 shows the slopes of the linear trends for the set of 68 wells. While groundwater levels have been more or less stable for most of the wells, there is a group of deep wells in the northeastern part of the county (circled in green) with declining trends. Groundwater levels in this area have declined on average between 100 to 150 ft. over the past 60 years. This group belongs to basin and range basin-fill aquifers and lies within the Anza-Borrego Desert State Park. The only water body nearby is the Clarke Lake, and a few small creeks. The local climate is arid, with low rates of groundwater recharge, resulting in unsustainable groundwater withdrawals. Cluster B Cluster A Figure 8. Slopes of linear fit for the 68 wells with at least 20 years of data Apart from the region in the northeast, most of the wells in San Diego County show mild declines or no significant trend between 1949 and It is possible that groundwater extraction along the 8

10 coast is balanced by seawater intrusion. Future studies can address this by examining groundwater quality, especially chloride concentration in coastal aquifers. 1.3 Historic Precipitation Precipitation in San Diego County has high inter-annual variability, ranging between 5.3 and 30.2 in/yr (133 and 767 mm/yr) from 1949 to 2009 (Figure 9). There is also high spatial variability, with an average of 6 to 12 in/yr along the coast, up to three times as much in the higher topography regions, then decreasing to 3 to 6 in/yr east of the mountains. Based on our assessment of the connection between climate and groundwater, precipitation tends to have a more immediate effect on water level in shallow wells (30 ft. or less). There is minimal observed correlation between interannual precipitation and deep wells (200 ft. or more). However, as surface water is the primary local water source, precipitation plays a role in annual water availability. Figure 9. Annual precipitation averaged over San Diego County between 1949 and The 10- year moving average is shown in red. 1.4 Drought Vulnerability We developed two risk metrics to capture the effect of within year dry periods (Normalized Deficit Index - NDI) and of drought across years (Normalized Deficit Cumulated - NDC). The Water Risk Indices presented here (see references 4, 5 for detailed computation) are based on the sequent peak algorithm originally developed for reservoirs. It quantifies the water storage capacity needed to meet the demand for a given sequence of supply 6,7,8. The daily water deficit is defined as the difference between the daily water demand and the daily renewable water supply. The deficits are accumulated while setting negative accumulations to zero. The maximum accumulated deficit in a given year divided by the average annual rainfall across the historical period is the NDI for that 9

11 year. Similarly the NDC is the maximum accumulated deficit for all 61 years divided by the average annual rainfall. The NDI is computed as one number for each year using historical daily rainfall data for the area and current daily water needs. It measures the maximum cumulated water shortage each year that needs to be provided for from ground or surface water storage or transfers from other areas. The deficit at the beginning of each year is set to 0 for the calculation of the NDI, but not for the NDC. The NDC is computed as one number over the historical climate record. It represents the largest cumulative deficit between renewable supply and water use over the entire period. Consequently, it reflects the stress associated with multi-year and within-year shortages at a location. An NDI or NDC greater than 1 represents the case where the cumulative deficit is greater than the average endogenous rainfall. The annual rate of consumption in these regions could be higher than the average utilizable rainfall rates. For San Diego, while NDI is relatively low (Figure 10A), NDC is around 2.39 indicating that San Diego requires greater than 2 times the average annual rainfall in storage to meet the stress; the rate of consumption is higher than the endogenously available water supply. Chronic or multi-year stress consequently emerges as the event of concern here. Using county data and restricting the definition of available supply to precipitation in the measured unit, the methodology effectively exposes the degree to which this city relies on external water transfers. Thus, potential spatial competition between cities and their hinterland is presented. If one could do a case by case analysis, one could identify the current sources being used, and the potential economic value of the transfer of use of the upstream water or water from groundwater storage to the stressed region to address the drought impact. The wavelet analysis (Figure 10B) on the time series of NDI provides some evidence for an episodic El Nino associated activity in the 5 to 7-year frequency band, especially around the strong ENSO events in and

12 Figure 10. (A) NDI time series for San Diego County, (B) wavelet power spectrum analysis 2. Green Infrastructure One might think that cities with relatively low annual precipitation, such as San Diego (~10 in/yr), do not have significant storm water pollution and contamination problems. There have been cases in San Diego County where public beaches are closed for up to several months due to contaminated runoff. 9 Stormwater collected from the streets, buildings, and gutters runs directly into the ocean and other surface water bodies untreated. Contaminants, debris, trash, and chemicals collect on impervious surfaces and accumulate over time during dry periods. The necessity to mitigate storm and urban runoff is apparent even in a city such as San Diego with relatively low precipitation. San Diego has implemented several programs to reduce the negative impacts of contaminated runoff. The Climate Protection Action Plan strives to make the city more resilient and robust against the impacts of climate change. The water related sections of the plan address water consumption, wastewater treatment and reuse. While stormwater management does not play a direct role in the Climate Protection Action Plan, the city recognizes the threats of climate change and values more sustainable operations. San Diego s Transportation and Storm Water Department focuses primarily on urban runoff mitigation and reducing Total Maximum Daily Loads (TMDL) of effluents that run into the bay, river and ocean. Through their Think Blue program the department educates and engages the public by attending community events and meetings. Think Blue s Public Information Officer, Lana Findlay, explained further that they conduct workshops and presentations, sponsor events, outreach to schools, and utilize [their] website, social media and advertising (TV, Radio, newspapers) to reach San Diegans with messages about pollution prevention. 10 Furthermore, Green Infrastructure, Low Impact Development and Best Management Practices also play a part in their outreach and education. Findlay spoke about the first successfully constructed green street on Mt Abernathy, which will be followed by other projects. Think Blue informs developers and contractors of the best methods to manage runoff. Think Blue illustrate the benefits of LID/ BMPs through display events, and Findlay hopes, the display will have take-away cards describing 9 LID BMPs in detail and will offer a physical and digital map of locations within the city where developers/contractors/architects can see real life examples of these structures after they have been built. As part of a larger pilot project for Think Blue, this effective stormwater runoff mitigation project was constructed on the corner of Logan Avenue and San Pasqual Street in San Diego (Figure 11). 11

13 Figure 11. Street corner bioretention basin in San Diego, CA As Figure 11 illustrates, the green infrastructure tools utilized in this project include swales, planters, catch basins and an inlet to the Chollas Creek. Rerouting the runoff from the roads into the basin reduces the amount of accumulated pollutants on impervious surfaces. With effective planning, implementation, and monitoring, these pilot projects will pave the way for additional GI developments. Another bioretential basin pilot project yielded a reduction in pollutants of 86%-87%(Table 1). Table 1. Table of anticipated load reductions from a bioretention basin at 43 rd Street and Logan Avenue, San Diego, CA. Overall, San Diego recognizes the inherent value in GI projects and with the help of Think Blue, the city is expanding its storm and urban runoff programs in an environmental and sustainable fashion. Another example of a pilot project is an infiltration project close to a beach parking lot (Figure 12). These pilot projects are evidence that San Diego is heading in the right direction when it comes to green, sustainable solutions to water quality and runoff. 12

14 Figure 12. Kellogg Park parking lot with green infrastructure vegetated separators, San Diego, CA. The planning document shows rows of parking space with vegetated separators and outlining used to detain, slow and retain a majority of the runoff. This is just one of many examples of how San Diego incorporates Green Infrastructure in their city planning Utility Rates As in many cities across the United States, customers in San Diego have seen an increase in their residential water bills over the last decade. In this study, survey responses from four water agencies serving approximately 1.8 million of the 3.2 million county residents are used to assess how water rates have changed over time. Each of the four water agencies responded to at least three American Water Works Association (AWWA) water rates surveys over a ten-year period. Accounting for annual inflation, rates increased on average 53% for the four utilities (Figure 13A) with the highest increase of 89% occurring for the 1.4 million residents served by the San Diego Water Department. Three of the four utilities employ an increasing-block rate structure whereby the residents pay a higher price in accordance with increased levels of consumption. This is a progressive rate-making strategy utilized in many water-scarce regions, especially in the southwest US, that encourages conservation. However, the benefit of affordability and conservation of increasing-block rate structures also leads to revenue instability, rendering the utility more dependent on sales 12. The fourth utility assessed in this study employs a uniform rate structure independent of consumption levels, and also has the highest residential water rate of the four utilities. A reliance on sales for cost recovery could be troublesome to water managers in San Diego County as total water sales have fallen on average 19% for the four utilities from their first reported levels during the time period (Figure 13B). The largest decline in total sales occurred between 2008 and 2010 for the San Diego Water Department which has seen the largest increases in total charges. While these rate increases and consumption decreases affect net operating revenues for San Diego, they may be positive from a physical sustainability perspective, especially during drought. Additionally, water conservation equates to energy conservation for the 13

15 county where the transportation of water is nearly three times more energy intensive than in Northern California. The upcoming desalination plant will mean a large increase in energy demands for San Diego. 12 A B Figure 13. (A) Total charge per 1500 cf water, and (B) Annual total water sales for four water utilities in San Diego County. All past rates have been adjusted for inflation to 2012 monetary units. Analyzing the price elasticity of demand (E) does not offer a uniform picture of how residential customers respond to increasing prices with the four utilities showing multiple years of inelastic ( E < 1) and multiple years of elastic ( E > 1) demands (Figure 14). Normalizing the demand by finding the amount of Total Water Sold per Population Served prior to finding the elasticity of demand offers a somewhat clearer picture with a greater number of elastic time periods and overall increasing elasticity among three of the four utilities (Figure 15). 14

16 Figure 14. Price Elasticity of Demand (E) between surveys from Figure 15. Price Elasticity of Normalized* Demand (E n ) between surveys from *Amount of Total Sold Water is normalized over the Total Population Served prior to finding the Elasticity One might assume that most of the ire for the sharp increase in water rates seen over the last decade would come from the residential customer than from the water managers. The utilities, after all, have to recover money not made in the declining water sales to provide for capital-intensive projects such as the Carlsbad desalination plant in progress. However, in a unique set of circumstances, it is the overseer of the water utilities, the San Diego County Water Authority, which is going to court to reduce water rates for customers. In two lawsuits filed in 2010 and 2012, the San Diego County Water Authority is suing the Metropolitan Water District of Southern California on what it claims are illegal water rates associated with the transportation costs of the delivering water to the county from the Colorado River water supplies. Superior courts in California have recently 15

17 completed the hearing of the first lawsuit, which ended on December 23, 2013 and a final ruling is expected in May The outcome of the trial will be a significant as it shows the diligent efforts of water managers assessing the true value of water service to the customer. 16

18 References 1 City of San Diego Water Utilities. 2 San Diego County Water Authority, 3 Richman, B. T. (1983), Budget boosts overall research but cuts NOAA and USGS funds, Eos, Transactions American Geophysical Union, 64(7): Devineni, N., Perveen, S., Lall, U (2013), Assessing chronic and climate induced water risk through spatially distributed cumulative deficit measures: A new picture of water sustainability in India, Water Resources Research, doi: /wrcr Chen, X., N. Devineni, U. Lall, H. Zenchun, D. Leihua, J. Qin, W. Jiahu and W. Shicheng (2013), China s Water Sustainability in the 21st Century: A Climate Informed Water Risk Assessment covering Multi-Sector Water Demands, Hydrology and Earth System Sciences, Discussion 10, , Lall, U. and C. W. Miller (1988), An optimization model for screening multipurpose reservoir systems. Water Resources Research. 24(7): Loucks, D. P., Stedinger, J. R., and Haith, D. A. (1981), Water resource systems analysis. Prentice-Hall, Englewood Cliffs, N.J. 8 Thomas Jr., H.A., R.P. Burden (1963), Operations Research in Water Quality Management, Harvard Water Resources Group, Cambridge, Mass (1963), pp San Diego CoastKeeper. Accessed August 2013: 10 Lana Findlay, Public Informations Officer Think Blue Program. 11 Kellogg Park, Green Lot Infiltration Project. City of San Diego, California. Think Blue Program Beecher, Janice and Chesnutt, Thomas. Declining Water Sales and Utility Revenues A Framework for Understanding and Adapting. Alliance for Water Efficiency, Wolfram, Catehrine and Zetland, David. Water conservation s other benefit: It s a power saver Los Angeles Times. March 3,