Salinas Valley Water Table Elevations: A Visualization Using GIS

Transcription

1 Salinas Valley Water Table Elevations: A Visualization Using GIS A Capstone Project Presented to the Faculty of Earth Systems Science and Policy in the Center for Science, Technology, and Information Resources at California State University, Monterey Bay in Partial Fulfillment of the Requirements for the Degree of Bachelor of Science By April McMillian May 8, 2003

2 Table of contents 1 ABSTRACT INTRODUCTION Groundwater The Salinas Valley Seawater Intrusion Salinas Valley Water Project Historical Benefits Analysis Water Table Visualization HYDROGEOLOGY OF THE SALINAS VALLEY SVIGSM inputs/model construction Model Inputs and Aquifer Properties: Model Calibration and Validity METHODS Data Collection Data Analysis Animation 1: Monterey Bay to Forebay Sub-area Animations 2: Upper Valley Sub-area Animations 3 and 4: Defined Contours Land use MPEG 4 Animation Formatting RESULTS Animation 1: Monterey Bay to Forebay Sub-area Animation 2: Upper Valley Sub-area Animation 3: Defined Contours Animation 4: Defined Contours Land Use DISCUSSION Animation Animation Climate Animation Animation Land Use Seawater Intrusion and the Salinas Valley Water Project: Other Management Uses Possible errors in study CONCLUSION ACKNOWLEDGEMENTS LITERATURE CITED APPENDIX

3 SALINAS VALLEY WATER TABLE ELEVATIONS: A VISUALIZATION USING GIS 1 ABSTRACT Policies and water management plans are currently in development and practice for many groundwater systems throughout California to help identify, control, and predict problems with depleting groundwater systems. The Salinas Valley Integrated Ground and Surface Water Model (SVIGSM) was used to quantify the impacts that various management alternatives would have on the groundwater aquifers within the Salinas Valley groundwater basin. Water table elevations from the SVIGSM output were color contoured and mapped for consecutive years from 1949 through The animation shows the changes the Salinas Valley water table has undergone from the years 1949 through Four animations were created from these maps. Animation 1 includes the Monterey Bay to the Forebay sub-area, and is mapped from 1949 through Animation 2 shows the Upper Valley sub-area only, mapped from 1949 through Animation 3 is of the lower Salinas Valley and coastal areas, mapped from 1949 through 1957 with a contour line showing the location of sea level within the water table. Animation 4 shows the same area as in Animation 3, mapped from 1980 through 1994, showing a contour at 10 feet below sea level. In Animation 1, water table elevations declined in the lower Salinas Valley and coastal areas during period of 1949 to 1957, and from 1983 to In the Upper Valley, water table elevation estimates remained relatively stable through time, with minor changes due to precipitation. Increases in the water table elevations are shown in all animations for the operation of the Nacimiento and San Antonio reservoirs. Water table elevations followed changes in precipitation during the period of 1957 through By understanding how groundwater elevations have changed over time, predictions and water management policies can be made to help the quality and longevity of groundwater systems in the Salinas Valley. 3

4 2 INTRODUCTION 2.1 Groundwater With global population increasing rapidly, groundwater resources are becoming overused and depleted. Groundwater is the source of more than 50% of the world s drinking water supplies, with many cities entirely depending upon groundwater for municipal, industrial, and agricultural uses (Cech, 2003). The construction of groundwater wells has increased greatly during drought years, due to the inability of surface water to meet water needs during droughts (CA DWR, 2000). Use of surface water has also declined recently due to increased protection of fish, bird, and riparian habitats in rivers and reservoirs (Ashley & Smith, 1999). With increasing dependence on groundwater aquifers for water supply, damages to groundwater aquifers and systems are likely to occur in the near future. When the amount of pumping from groundwater aquifers is greater than the amount of recharge, water table elevations within aquifers will decline (Cech, 2003). Other problems with declining water table elevations, or overdraft aquifers, include land subsidence and instability, water quality deterioration, seawater intrusion, well abandonment, and structural damage (Larson, et al., 2001). By identifying overdraft conditions, steps can be taken to protect the quality and longevity of groundwater supplies. Identifying overdraft conditions can be done visually using water table elevation mapping and comparisons over time. 2.2 The Salinas Valley The Salinas Valley in Monterey County, California has among the largest groundwater users in California. The Salinas Valley is unique in California in that it is not connected to the California State Water Project aqueduct system, relying mainly on the Salinas River and groundwater basin for water supplies (CA DWR, 2000). Increasing population within the Salinas Valley is likely to have a large impact on the groundwater aquifers within the Salinas Valley basin. Over the past 50 years, population in the Salinas Valley has risen significantly. Since 1950, population has increased by over 200% (USCB, 2001), and is estimated to increase an additional 35% by the year 2020 (Monterey County, 2001). It is estimated that through this population increase, over 40,000 additional housing units will be required to sustain the growth (Landwatch, 2002). This new development will create further strain on the groundwater levels of the Salinas Valley basin. 4

5 Though municipal development is an important issue with water supplies, agriculture is the main use of groundwater in the Salinas Valley, using most of the groundwater resources (Planert & Williams, 1995). With such high demands on the groundwater supply, the Salinas Valley groundwater table elevation has likely declined over the past 50 years. This has created problems such as loss of water supply, seawater intrusion, and well-abandonment within the valley. 2.3 Seawater Intrusion Seawater intrusion is a problem occurring in many aquifer systems that are connected directly to the ocean. Because freshwater is less dense than saltwater, the freshwater creates a layer overlying the saltwater. The depth of the freshwater to the saltwater is equivalent to about 40 times the depth of the water table to sea level. If the water table falls below sea level, the separation is removed (Viessman & Lewis, 1995). This can occur when pumping causes the water table in an aquifer to fall below sea level, causing seawater to enter pumped wells (Figure 2.1). The increasing the chloride content of the water supply creates problems for drinking and agricultural use. Native groundwater typically has a chloride content of 0.05g/L, with ocean water having a content of 35g/L (Bear, et al., 1999). The Monterey County Water Resources Agency uses the chloride levels stated by the California Safe Drinking Water Act of 0.5g/L limit to whether or not an aquifer at a certain point is intruded with seawater (SVWP, 2002). Figure 2.1: Seawater Intrusion example (Skinner & Porter, 1995) Seawater intrusion was first recognized as a problem in the Salinas Valley as early as the 1930 s. In 1946, the California Department of Water Resources prepared Bulletin 52, the Salinas Basin Investigation. This report provided a basis for solving groundwater overdrafts and seawater intrusion problems within the valley. From this, the Monterey County Water Resources Agency constructed two reservoirs along tributary rivers of the Salinas River: the Nacimiento and San Antonio reservoirs. These reservoirs were constructed for flood control and to increase 5

6 recharge to the groundwater basin from summer releases into the Salinas River (Montgomery Watson, 1998). Though these reservoirs have been in operation for over 40 years, seawater intrusion has continued to spread inland, causing water quality deterioration and wellabandonment. By 1999, seawater intrusion was estimated to affect an area as much as 24,019 acres in the upper aquifers of the north Monterey county coastal areas (Figure 2.2). Figure 2.2: Estimated Seawater Intrusion of the 180-Foot Aquifer (Source: MCWRA) 6

7 2.3.1 Salinas Valley Water Project The Salinas Valley Water Project was developed by the Monterey County Water Resources Agency and the Army Corps of Engineers to develop methods to 1) stop seawater intrusion, 2) provide adequate water supplies to meet current and future needs (year 2030), and 3) improve the hydrologic balance of the groundwater basin of the Salinas Valley. The project proposes several options for reducing groundwater withdrawals from the basin and increasing recharge to the groundwater aquifers. Options are the construction of a diversion facility in the lower Salinas River to supply irrigation water and use of recycled wastewater as a part of the Castroville Seawater Intrusion Project for irrigation and recharge supply (SVWP, 2002) Historical Benefits Analysis The Salinas Valley Historical Benefits Analysis (HBA) was created to identify the benefits of increasing recharge to the Salinas Valley, and to make a comparison of benefits of the reservoirs. Benefits of the reservoirs include hydrologic benefits, flood control benefits, and economic benefits (Montgomery Watson, 1998). In order to quantify the hydrologic benefits to the Salinas Valley, such as higher groundwater levels, reliable groundwater supplies, better operation of wells, and higher groundwater quality, the Salinas Valley Integrated Ground and Surface Water Model (SVIGSM) was developed. This model was developed in 1993, and revised in 1995, in order to provide a better understanding of the Salinas Valley groundwater basin system and processes. The SVIGSM includes aquifer data from the years 1949 through 1994, and land use from 1970 to 1994 (Montgomery Watson, 1997). One of the outputs created by this model is estimated water table elevation of the Salinas Valley basin from Water Table Visualization Mapping the water table elevation is a useful tool for understanding and connecting the movements and changes within groundwater aquifers, and relationships with land use and development. An example of this is shown in the Mojave Desert in Southern California. Stamos, Nishikawa, Martin, and Cox of the US Geological Survey (2001) used past groundwater table levels to visually estimate how artificial recharge can increase the groundwater aquifer level. Using well data from the years , they created maps showing the water table level contours within the Mojave River Basin. From these contour maps they estimated future behaviors of the basin. They developed an animated color model on how groundwater levels can 7

8 increase or decrease over the next 20 years for both with and without artificial recharge. An example of one contour map is shown in Figure 2.3. The animated contour maps from the model allowed the Mojave Water Agency to view the behaviors of the water table if artificial recharge is applied, versus if it is not (Stamos, et al. 2001). Figure 2.3: Simulated water level change between 1999 and 2019 without artificial recharge. Red areas signify a greater change in the depth of water level. (Source: Stamos, et al. 2001) Using this type of visualization technique would be beneficial for the management of the Salinas Valley groundwater basin. By creating this map, the behavior of the groundwater system is visualized in a context that is easy for many people to understand. Creating a similar map of groundwater table contours as Figure 2.3 would be useful for the Salinas Valley in visualizing the historical behaviors of the groundwater system, and to predict what the future levels will be like. This can be created using the modeled water table elevation estimates from the output of the SVIGSM. 3 HYDROGEOLOGY OF THE SALINAS VALLEY The Salinas Valley is a northwestern trending coastal valley drained by the Salinas River along the central coast of California. The Salinas River extends through the valley about 150 miles from its headwaters in San Luis Obispo County to the Monterey Bay, draining an area of about 4,500 square miles (USGS, 2002). The Salinas Valley groundwater basin extends about 120 miles southward from the Monterey Bay, and is bordered to the south by the La Planza Range, to the west by the Santa Lucia Range, northwest by the Sierra de Salinas Range, east by 8

9 the Diablo Range, and northeast by the Gabilan Range. The basin is mainly filled with semi- and unconsolidated alluvial sediments, bordered and underlain by metamorphic and igneous rocks. The elevation of the Salinas River near Santa Margarita is about 1,200 feet above sea level, and the gradient decreases gradually down the Salinas Valley to sea level in the Monterey Bay (Planert & Williams, 1995). The main source of recharge to the groundwater basin is the Salinas River. The Salinas River flow is managed by reservoirs on tributary streams, mainly the Nacimiento reservoir (constructed in 1956 along the Nacimiento River) and San Antonio reservoir (constructed in 1967 along the San Antonio River), to provide year-round flow to the river for groundwater recharge (Mills, et al., 1988). Additional recharge sources include precipitation, urban and agricultural runoff, and tributary stream flow. Tributaries to the Salinas River in addition to the Nacimiento River and San Antonio River include the Estrella River, Paso Robles Creek, Atascadero Creek, Arroyo Seco, San Lorenzo Creek, Chualar Creek, El Toro Creek, as well as other small creeks from the surrounding mountain ranges. About 87% of the precipitation falls November through April in the Salinas Valley, ranging from inches per year depending on elevation ( USGS Water Atlas, 2001). The Salinas Valley basin is divided by the Monterey County Water Resources Agency into hydrological sub-areas: the Pressure, East-Side, Forebay, and Upper Valley as well as the Monterey Bay and Fort Ord/Toro sub-areas (Figure 3.1). There are four main aquifers throughout most of the basin: the unconfined, 180 foot deep, 400 foot deep, and 900 foot deep, separated by confining units of clay and silt (Munévar and Mariño, 1999). The Upper Valley sub-area consists mainly of a single unconfined aquifer, and the Forebay and East-Side sub-areas consists of the 400-foot and 900 foot deep aquifers. The Pressure sub-area consists all three aquifers, extending into the Monterey Bay. 9

10 Figure 3.1: Salinas Valley groundwater basin and hydrologic sub-areas. 3.1 SVIGSM inputs/model construction Montgomery Watson Consultants developed the Salinas Valley Integrated Ground and Surface Water Model for the Monterey County Water Resource Agency as apart of the Historical Benefits Analysis. The model is a three-dimensional, finite difference model, created with an irregular grid of 1,760 nodes (Figure 3.2). Figure 3.2: Sketch of SVIGSM grid (left) and node point locations (right) Model Inputs and Aquifer Properties: Crop potential evapotranspiration was estimated using the California Irrigation Management Information Stations, 16 of which are within the basin and correlated to sub-areas within the model. These values were based on the California Department of Water Resources Bulletin Potential evapotranspiration values were obtained for six crop groups for each sub-area of the model. Crop groups include pasture, sugar beets, field crops, truck crops, orchard and vineyard. Crop irrigated acreage, crop potential evapotranspiration, effective precipitation 10

11 (daily), and irrigation efficiency are all calculated as apart of total agricultural water use. Riparian water use for phreatophytic vegetation types were estimated using consumptive use and total area of the riparian corridor of the Salinas River based on 1994 orthophotographic maps. Land use was determined using surveys by the Department of Water Resources in 1968, 1976, 1982, 1989/91 and MCWRA 1995 surveys. Land use reports include the acreage of agricultural, urban, native vegetation, and riparian vegetation. Irrigation efficiency was estimated mathematically, with in between rotation cropping practices of truck crops accounted for. Urban water use and groundwater pumping values were obtained from local water agencies. Other model inputs include pump efficiency and hydraulic conductivity. These values were obtained from the Ground Water Extraction Management Database, maintained by the Monterey County Water Resources Agency (Montgomery Watson, 1997) Model Calibration and Validity The SVIGSM was calibrated for the period October 1969 through September 1994, where the regional parametric grid is numerically overlaid on the model grid for comparison. The period of October 1969 through September 1994 for the calibration period reflects both wet and dry hydrologic cycles, the majority of groundwater level measurements, and the operation of both the Nacimiento and San Antonio reservoirs (Montgomery Watson, 1997). Output comparisons were made to the following values: water levels at 64 wells and seawater intrusion contours with chloride trends over time. To compare stream-aquifer interactions, a stream recharge index for the Salinas River is used at two reaches: from Bradley to Soledad and from Soledad to Spreckels. Adjustments were made to hydraulic conductivity values and streambed thickness until the model was deemed acceptable (Montgomery Watson, 1997). The results of the model calibration for water table elevations for each sub-area are summarized in Table 3.1. Though the summary of the SVIGSM calibration results show little difference between the modeled water table elevation and the well data, a large difference is seen in linear graphs. The majority of the graphs show the model overestimating the water table elevation from the calibration wells, with scatter. Examples of the graphs comparing the SVIGSM output to the calibration well data are shown in the Appendix. 11

12 Sub-area Accuracy % Of Time Pressure East-Side Forebay Upper Valley ± 5ft 38% ± 10ft 70% ± 5ft 30% ± 10ft 57% ± 5ft 55% ± 10ft 80% ± 5ft 50% ± 10ft 80% Table 3.1: Summary of SVIGSM water table elevations, compared with real well data, 1969 through 1994 (Source: Montgomery Watson, 1997) 4 METHODS 4.1 Data Collection The output water table elevations from the Salinas Valley Integrated Ground and Surface Water Model (SVIGSM) were used to construct the maps for the animations. The Monterey County Water Resources Agency prepared a file containing groundwater table elevations derived from the 1,726 nodes of the SVIGSM. The groundwater elevations were averaged (by water years, October to September) to yearly values from the years 1949 through 1994, and averaged for all groundwater aquifers within the Salinas Valley basin. All elevations were adjusted to mean sea level. In addition to the groundwater levels, the Monterey County Water Resources Agency provided GIS shapefiles of the hydrologic sub-areas of the Salinas Valley, basin boundary, model grid, and node locations within the valley. Precipitation data for the Salinas Valley were obtained from the National Climatic Data Center, a climate data archive available online through the National Oceanic and Atmospheric Association. Total monthly precipitation (in inches) under California Region 4, which includes Monterey County, was collected for the years 1948 through 1994 (NCDC, 2003). GIS shapefiles of California Counties and California major roads and freeways were obtained from the ESRI Data & Maps (1998), available with ArcView 3.2, to define the boundaries of Monterey County. A shapefile outlining of the State of California, and major rivers within California was obtained from Geography Network online, originally created by the US Geological Survey (2002). 12

13 Land use for the Salinas Valley was determined using a previously constructed land use raster file, created by the Central Coast Watershed Studies, or CCoWS (Newman et al., 2003). 4.2 Data Analysis Animation 1: Monterey Bay to Forebay Sub-area Using the SVIGSM output water elevation, several water level contour maps were created using ArcGIS 8.2 Geographical Information Systems software, manufactured by ESRI. The point shapefile containing the node locations (received from MCWRA) was exported from ArcMap (a mapping tool in ArcGIS) and brought into Microsoft Excel, where the Northing and Easting coordinates could be applied to the water elevation estimates. The estimates were then separated into two files, containing estimates for Animation 1 (Monterey Bay to Forebay subarea) and Animation 2 (Upper Valley Sub-area). The two separate files were exported from Excel to ArcMap to create each animation separately. Also within Excel, the minimum water table elevation for each year were graphed over time. For each year from 1949 through 1994 using the Monterey Bay to Forebay water table estimates, Triangulated Irregular Networks, or TINs, were created in ArcMap. TINs are an estimated continuous surface created by interlinking triangles between points representing different elevations. By doing so, elevations between known values are estimated, allowing contour lines to be created (Booth, 2000). The TINs created from the water table elevations were clipped using the basin boundary shapefile, in order to contain the contours within the limits of the Salinas Valley basin. Color legends were manually created for each TIN to maintain consistent color gradients for all of the years. The legend breaks were manually created to allow a more detailed analysis in the lower water table elevations (-70 through 100 feet), and less detail in the upper elevation values, which are most likely associated with the rising ground surface elevation increasing south towards the Upper Valley (200 through 1200 feet). The base legend colors were developed using the year 1992, which contained the lowest groundwater elevations. Dark red colors represent lower water elevations; green and blue represent higher water elevations. The TINs for each year were exported into jpeg images using a consistent layout template for all mapped years. The legends were excluded from these layouts every year except The image containing the 1992 map and legend was imported into Adobe Photoshop 5.5, where the legend was cut into a separate image file to allow the 1992 legend to be applied to all years. 13

14 Using Microsoft PowerPoint, each year s jpeg image was imported as a background image of a blank slide. The individual 1992 legend file was imported into the slide master, allowing it to appear in the same position on every slide. All slide transitions were timed at onesecond intervals, creating the animation of the Salinas Valley water table elevation from the Monterey Bay to the Forebay sub-area Animations 2: Upper Valley Sub-area A second animation containing water table elevations for the Upper Valley Sub-area was created using similar methods as Animation 1. The file containing the Upper Valley Sub-area elevations was imported into ArcMap. TINs were created for each year ( ) using the clipped sub-area boundary, and consistent color gradients were manually created for each year. Each TIN was exported as a jpeg file using a consistent layout template, without legends except for the year 1950, which has the lowest water table values. Each image was applied to PowerPoint slides using the same methods and slide transition times as for Animation 1, and the legend for the year 1950 applied to all slides Animations 3 and 4: Defined Contours Using the same individual TINs created for Animation 1, Animations 3 and 4 were created. Within ArcMap, these TINs were magnified to show the northern half of the Pressure and East-Side sub-areas of the Salinas Valley basin. Using the same layout template for Animation 1, these new maps were exported as jpeg image files and placed into PowerPoint slides using the same methods and slide transition times as Animation 1. Within PowerPoint, specific contour lines were drawn into the individual slides containing the maps placed as background images. For the years 1949 through 1957, a solid black contour line was drawn at the zero-foot color contour break to represent the position of sea level in each slide. The slides for these years create Animation 3. For the years 1980 through 1994, a solid black line was drawn at the 10-feet below sea level color contour break for each slide. These slides create Animation Land use To compare land use of the Salinas Valley to the mapped water table animations, the TIN created for 1994 in Animation 1 was placed on top of the land use file provided by CCoWS within ArcMap. The transparency of the land use file was varied to allow the land use colors to be viewed through the TINs color contours. Individual layout images were exported as jpeg files 14

15 as needed. For cases when the transparency of the TIN did not show the contours well, individual contour lines were drawn in Microsoft Word on top of the land use jpeg images to define where color contours would have been MPEG 4 Animation Formatting Each animation was converted into mpeg 4 (.mp4) and QuickTime (.mov and.avi) movie formats to reduce the file sizes and allow for faster downloading from the Internet site listed under Results. The cut legends from the year 1992 of Animation 1 and Animation 2 attached to the corresponding TIN using Adobe Photoshop, and individual contour lines for Animations 3 and 4 were drawn into the images. The final images were exported as individual jpeg files. These images were imported into the software Apple QuickTime Pro under a number sequence and exported as mpeg 4 and QuickTime movie/avi file formats. 5 RESULTS 5.1 Animation 1: Monterey Bay to Forebay Sub-area Animation 1 shows the general trends of the groundwater table level within the Salinas Valley, representing the Forebay sub-area to the Monterey Bay through the years of 1949 to The animation file can be viewed at the website The darkening of the red colors indicates falling of the groundwater table elevation. The graphed minimum water table values also show the rise and fall of the elevations, shown in Figure 5.1. Water Table elevations are shown declining in both Figure 5.1 and Animation 1 from the years 1949 through 1957, 1958 through 1962, and 1983 through The years 1967 through 1981 show varying changes in the groundwater table elevations. Lower water table elevations also decrease up the valley, and a low water table gradient is protruding into the Monterey Bay. 15

16 0 Yearly Minimum Values: Animations 1,3,4-10 Water Table Levels feet above sea level Nacimiento (1956) San Antonio (1967) -80 Figure 5.1: Minimum water table elevation simulated by SVIGSM by year, from the Monterey Bay to Forebay sub-area 5.2 Animation 2: Upper Valley Sub-area Animation 2 shows the changing groundwater table elevation for the Upper Valley Subarea. As with Animation 1, areas of dark red show lower water table elevation. The animation file can be viewed at The graph of minimum water table values for the Upper Valley Sub-area is shown in Figure 5.2. Both the animation and graph show a slow overall increase in elevations from 1950 through Water table elevations decrease from 1987 through 1992 and increase through There is no cone of depression shown in this animation, though lower water table elevations are present at the north end of the sub-area. 16

17 230 San Antonio (1967) Yearly Minimum Values: Animations 2 Water Table Elevation feet above sea level 220 Nacimiento (1956) Figure 5.2: Minimum water table elevation simulated by the SVIGSM by year, for the Upper Valley Sub-area. 5.3 Animation 3: Defined Contours Animation 3 shows a closer look at the groundwater table elevations in the lower Salinas Valley and coastal areas for the years 1949 through The animation file can be viewed at the website In addition to the magnification, there is a solid black line drawn at the zero-foot contour line color break. The black sea level line shows the movement of groundwater at that elevation, defining where seawater intrusion may be a problem. 5.4 Animation 4: Defined Contours Animation 4 shows a closer look at the groundwater elevations in the lower Salinas Valley and coastal areas for the years 1980 through The animation file can be viewed at The line drawn at 10-feet below sea level shows the changes that groundwater has undergone, in a different perspective than the colors may show. The declining groundwater elevations are shown not only as darkening red colors, but the increasing size/widening of the black contour line. Water table elevations for the years 1981 through 1983 increase, and decrease from the years 1983 through

18 5.5 Land Use in Figure 5.3. The comparison of the 1994 water table level to land use in the Salinas Valley is shown Figure 5.3: Comparison of 2003 Land use and water table elevation of 1994 from Animation 1. The lower water table elevations shown by the dark red colors correspond to the bright yellow colors in land use, representing the urban areas of the city of Salinas, and surrounding crop agriculture, shown in pink colors on the land use map. 18

19 6 DISCUSSION 6.1 Animation 1 As stated in the Results, Animation 1 shows the rise and fall of the Salinas Valley groundwater table elevation from 1949 through Animation 1 represents the lower Salinas Valley coastal areas to the Forebay sub-area. A cone of depression is visible near the eastern boundary of the basin, near the city of Salinas (Figure 6.1). Cone of depression Figure Groundwater table elevation (feet) with general city locations (shown in Animation 1). The graph of minimum groundwater table values shown in Figure 5.1 shows increasing and decreasing minimum elevations over time. This representation can be used for Animation 1, due to the minimum water table elevation being within the same general location as shown in the animation. Figure 5.1 shows declining levels from 1949 through In 1958 there is an increase in water table elevation. This may correspond to the construction and operation of the 19

20 Nacimiento Reservoir in Water table elevations continue to decline again until 1962, after which they increase variably until The San Antonio Reservoir was constructed and began operation in 1967, which may be represented in the increasing water table elevation. Water table elevations decrease from 1974 through 1977, and are variable through Elevations increase until 1983, and then generally decline until Animation 2 Animation 2 shows the changing groundwater table elevation for the Upper Valley subarea only. Water table elevations are shown at higher values than Animation 1, due to the higher elevations in the Upper Valley areas. There is no cone of depression visible in this animation, though lower water table values are present at the north end of the sub-area. Little change is shown in the animation, through the darkening of the red colors, or lowering water table elevations. In comparing the minimum water table values graphed in Figure 5.2 (Animation 2) to Figure 5.1 (Animation 1), a different pattern of change over time is shown shows the lowest water table elevation, instead of 1992 with Animation 1. The water table shows a general increase in elevation over time, though variable. 6.3 Climate Both Animation 1 and Animation 2 show the water table elevation fluctuate over the time period between 1949 through Though they show a general trend of either increasing or decreasing, the changes are not consistent. One possible explanation for the variability is climate, specifically changes in total annual precipitation. The main sources of recharge for the Salinas Valley groundwater aquifers are streamflow percolation from the Salinas River and percolation from precipitation. Total annual precipitation collected from the National Climatic Data Center for the years 1949 through 1994 are compared to the minimum values of both Animation 1 (Figure 5.1) and Animation 2 (Figure 5.2) to find similar patterns and possible explanations for the changing water table elevations over time. For Animation 1, the climate and minimum water table elevations are shown in Figure

21 45 Minimum Water Table Elevation and Precipitation (Animation 1) 0 Annual Precipitation inches Nacimiento (1956) San Antonio (1967) Precip Forebay Water Table Elevation feet above sea level Figure 6.2: Minimum water table elevation from Animation 1 compared with total annual precipitation from 1949 through Figure 6.2 shows the overall decreasing water table elevation, as described under Figure 5.1. When comparing the minimum water table elevation with total annual precipitation, the declining trends are better shown. The precipitation data for the time period varies through the time period, but the average remains relatively constant. Between the years of 1949 through 1962, minimum water table elevation of Animation 1 decreases substantially. The precipitation patterns through the same time period remain relatively constant (increases and decreases by similar amounts). This is directly visible for the year 1961 through 1962, where precipitation is increasing, and water table levels are decreasing. The years 1963 through 1980 show similar patterns with precipitation and minimum water table elevation. A similar comparison is made with minimum values from Animation 2 (Figure 5.2) and the total annual precipitation. The comparison is shown in Figure 6.3. The patterns of the minimum water table elevation in Animation 2 roughly correspond to changes in precipitation. Figure 6.3 shows that the Upper Valley sub-area is relatively stable in terms of the groundwater table. There is little fluctuation of the water table over time, with changes in precipitation occurring. The Upper Valley sub-area receives maximum benefit from the operation of the two reservoirs, at Nacimiento River and the San Antonio River. What this graph and Animation 2 show is that the releases into the Salinas River from the two reservoirs are successful in 21

22 maintaining the groundwater table elevation in the Upper Valley sub-area. Elevations decline form the years 1986 through 1991, but correspond with low precipitation for that time period. Annual Precipitation inches Precip Upper Valley Nacimiento (1956) Minimum Water Table Elevation and Precipitation (Animation 2) San Antonio (1967) Water Table Elevation feet above sea level Figure 6.3: Minimum water table elevation from Animation 2 compared with total annual precipitation from 1949 through Animation 3 Using a solid contour line in an animation gives a different perspective on how the water table elevations are changing, by drawing the attention to the widening of that specific elevation, and shows the extent to which groundwater tables are increasing or decreasing. 22

23 Figure 6.4: Map of 1957 groundwater table elevations from Animation 3. Position of sea level within the groundwater table is drawn in black. The use of sea level for drawing the contour line is linked to seawater intrusion. Since seawater intrusion occurs in coastal aquifers when the water table falls below sea level, locating where sea level is in the water table is useful for predicting where problems can occur. 6.5 Animation 4 Using the color break of 10-feet below sea level for Animation 4 not only shows the movement of the groundwater table below sea level, but the reversing gradient from the cone of depression (west to east) east of the city of Salinas to the Monterey Bay (east to west). An example of this is shown in Figure

24 Figure 6.5: Map of 1992 groundwater table elevations from Animation 4. Position of 10 feet below sea level of the groundwater table is drawn in black. 6.6 Land Use Comparing land use to groundwater tables is useful to determine possible causes of the declines. The land use file obtained from CCoWS shows general land use of the Salinas Valley up to the beginning of Land use may have changed somewhat since 1994, most likely in increasing urban cities and vineyards along the edges of the Salinas Valley (personal communication with Wendi Newman, April 2, 2003). When comparing land use to the groundwater table mapped in Animation 1, several key connections are made. Figure 6.6 shows the land use map and contours of the groundwater table of 1994 from Animation 1. In the latter years of the animation, there is a large cone of depression forming along the eastern side of the valley near the city of Salinas. This depression is just east of the city boundaries outlined by the yellow colors in the land use map (Figure 6.6). The city of Salinas is also surrounded by mainly row crop agriculture (shown in pink in the land use map, Figure 6.6). The shape of the crop growth roughly corresponds to the outline of the cone of depression in the water table map (Figure 6.6). The large amounts of crop and vineyard 24

25 land use, in addition to urban land use, increase the amount of groundwater withdrawals in the basin Water Table Elevation 10-foot contour intervals, from 60 feet to 20 feet below sea level Figure 6.6: Land use compared with the groundwater table elevation of 1994 from Animation 1, drawn as contour lines from 60-feet to 20-feet below sea level. Land use in the Upper Valley is shown in Figure 6.7. Land use in the Upper Valley subarea mainly consists of grassland vegetation, with crops and vineyards in the northern Upper 25

26 Valley sub-area and along the Salinas River corridor. There is little urban land use in the Upper Valley as compared to the lower Salinas Valley. The differing land use between the Upper Valley and the Lower Salinas Valley sub-areas also correspond to the different water table elevations, estimated by the SVIGSM. With less cropland and urban land use, less water is withdrawn from the groundwater aquifers, creating relative stability in the elevation of the water table. Figure 6.7. Land use in the Upper Valley Sub-area. 6.7 Seawater Intrusion and Salinas Valley Water Project: As mentioned before, seawater intrusion was first recognized as a problem in the Salinas Valley groundwater aquifers as early as the 1930 s. Though two reservoirs have been 26

27 constructed, groundwater tables continue to decline. This is shown in Animation 1 as well as Figure 5.1. Animation 3 and 4 show that the groundwater table within the Salinas Valley are below sea level in the lower valley and coastal regions, suggesting possible links and causes to seawater intrusion. Municipal development around the city of Salinas and continued agriculture have caused increased demand on water supplies, creating further strain on the seawater intrusion problem. The Salinas Valley Water Project addresses the issues of seawater intrusion in the Salinas Valley by reducing pumping and increasing recharge to the groundwater aquifers. Components of the Salinas Valley Water Project include use of recycled water for irrigation, a diversion facility to divert water from the Salinas River for use, and adjusting the flow into the Salinas River from the Nacimiento and San Antonio reservoirs. These projects would assist in reducing the strain on the groundwater aquifers, and increases recharge to prevent further movement of the seawater intrusion front. The Historical Benefits Analysis was used to estimate the benefits of these proposed management alternatives to stop seawater intrusion. The SVISGM was used to quantify the benefits the operation of the two reservoirs has given to the groundwater aquifers. By mapping the groundwater elevations from the SVISGM estimates, the changes that groundwater table elevation has undergone are visualized. Animations 3 and 4 show the extent of the cone of depression east of the city of Salinas, and area of the water table that is below sea level. The animations show the rates at which groundwater elevations are declining, and their relationships to years of high and low precipitation amounts. 6.8 Other Management Uses Creating animations of the groundwater table of the Salinas Valley is not only useful for determining possible causes of seawater intrusion and overdraft, but has several other water management uses as well. These animations can be created to show benefits of varying recharge amounts (such as with the Mojave River basin), how rivers and streams can affect groundwater levels, and how groundwater levels react to other factors such as population growth. Color contour animations display groundwater table data in a way that many people can understand easily. The color maps show how groundwater behaves under varying conditions without displaying excess numerical data. People do not have to be experts on the subject to understand the maps, making them easier to present to wider ranges of audiences. The animation 27

28 of the maps show the extents of problems, how they have increased or decreased, and give the audience a different perspective on groundwater topography, movements, and behaviors. 6.9 Possible errors in study This study examines visually how the groundwater tables of the Salinas Valley have changed over time. Though the animations clearly show the water table elevations decreasing and the creation of a cone of depression, several factors may have introduced errors into the study. First, the groundwater estimates are not real data. The estimates mapped are from the Salinas Valley Integrated Ground and Surface Water Model, created as apart of the Historical Benefits Analysis with the Salinas Valley Water Project. By using modeled estimates, factors such as streamflow, precipitation, vegetation and crop water use, and hydraulic conductivity have been adjusted into the estimates. The estimates are also averaged for the 3 main groundwater aquifers within the Salinas Valley, the 180-foot, 400-foot, and 900-foot deep semiconfined aquifers. These aquifers have different pumping amounts, and are not continuous throughout the Salinas Valley basin. Also, as seen in the calibration well comparisons to the SVIGSM data (Appendix), the model results do not completely correlate to real well elevations. The majority of the data is within ±10-feet of the real data, as summarized in Table 3.1. Though the water table elevations mapped from the SVIGSM estimates may not directly correspond to the actual water table elevations, the patterns shown by the animations over the time period are similar, and problem areas are identified. The visualization technique was successful in identifying the areas where more research is needed. A third source of error within this study is when creating the maps, or TINs, for the water table elevations, the Salinas Valley basin was split to allow for closer analysis of the Upper valley and the lower valley/coastal areas. By creating two separate TINs, the boundaries in which the TINs are defined are different. If the valley were mapped as a whole, the northern border of the Upper Valley TIN series (Animation 2) would give different results. The differences between the two methods of mapping are minimal, and the focus of this report is on the lower valley/coastal areas where groundwater elevations are lowest. 28

29 7 CONCLUSION Creating animated groundwater table maps is useful for the visualization of problems occurring within groundwater aquifers. By placing the water table elevation data in a visual context, problem areas are better identified, and those problems can be clearer to understand by people who are not very familiar with the project and groundwater systems. If levels are decreasing in certain areas, then the maps and animations can show areas where more research is needed. Though the Salinas Valley has very large groundwater withdrawals, the Salinas Valley Water Project is working to halt seawater intrusion and protect the groundwater supplies to support the vast agriculture industry and rising populations of the valley. The Salinas Valley Integrated Ground and Surface Water Model helped decision-makers with the water project to quantify the benefits of the reservoirs and increasing recharge to the basin. Using the averaged output groundwater table elevation estimates from the model can assist in visualizing the extent of the declining groundwater table elevation problem in the animations, and can assist in showing benefits of recharge as well. A further step with these estimates and visualization method is to create more detailed animations with the output estimates from the individual aquifers (180-foot, 400-foot, and 900- foot). Creating similar animations with real well data will also give a more accurate picture and idea of how the groundwater table elevations have changed over time. Predictions can be made from these to estimate how the water table elevation will be affected in future years, with increased use, or with increasing recharge rates/amounts. Population around the world is continually increasing, creating higher demands on freshwater sources. Management of groundwater resources is crucial to the protection of groundwater aquifers and supplies. Groundwater table visualization is one possible method for learning more about the behaviors, changes, and identifying possible sources and solutions to groundwater problems. 29

30 8 ACKNOWLEDGEMENTS I would like to thank Howard Franklin and German Crillio of the Monterey County Water Resources Agency for the use of the SVIGSM estimates, reports, and assistance with the project development. I would also like to acknowledge Wendi Newman and Dr. Fred Watson of CCoWS, Lisa Edwards, Jennifer Edwards, Dr. Dan Shapiro, and Dr. Robert Curry for their assistance and ideas towards the project. And finally, I would like to thank Dr. Douglas Smith, for his ideas, support, and believing in this project. 9 LITERATURE CITED Ashley, J.S., Smith, Z.A. (1999). Groundwater Management in the West. Lincoln: University of Nebraska Press. Bear, J., Cheng, A.H.-D., Sorek, S., Ouazar, D & Herrera, I. (editors, 1999). Seawater Intrusion in Coastal Aquifers Concepts, Methods and Practices. Dordrecht: Kluwer Academic Publishers. Booth, Bob (2000). Using ArcGIS 3D Analyst. Redlands, CA: Environmental Systems Research Institute Inc. California Department of Water Resources ( CA DWR ), (2000). Preparing for California s Next Drought: Changes Since Retrieved on October 23, 2002, from: Cech, T.V. (2003). Principles of Water Resources: History, Development, Management and Policy. New York: John Wiley & Sons. ESRI (1998). US Major Roads by State, California. Created by Geographic Data Technology, available on ESRI Data & Maps 4 (CD). Landwatch, Monterey County (2002). Room Enough: A report on development in Monterey County. Retrieved on October 31, 2002, from: Larson, K.J., Başağaolğlu, H., & Mariño, M.A. (2001). Prediction of optimal safe ground water yield and land subsidence in the Los Banos-Kettleman City area, California, using a calibrated numerical simulation model. Journal of Hydrology, 242, Mills, T., Hoekstra, P., Blohm, M., & Evans, L. (1988). Time domain electromagnetic 30

31 soundings for mapping sea-water intrusion in Monterey County, California. Ground Water, 26(6), Monterey County (2001). Monterey County Draft General Plan Executive Summary, 21 st Century General Plan Update. Retrieved October 1, 2002, from: Monterey County Water Resources Agency (2001). Seawater Intrusion in the Pressure 180-Foot Aquifer Water Quality Data. Retrieved on February 13, 2003, from: Montgomery Watson Inc. (1997). Salinas Valley Integrated Ground Water and Surface Water Model Update. Final Report, prepared for the Monterey County Water Resources Agency. Montgomery Watson Inc. (1998). Salinas Valley Historical Benefits Analysis (HBA). Final Report, prepared for the Monterey County Water Resources Agency. Munévar, A., & Mariño, M.A. (1999). Modeling analysis of ground water recharge potential on alluvial fans using limited data. Ground Water, 37(5), National Climate Data Center ( NCDC ), (2002). Average Monthly Precipitation Data, Division 04. National Oceanographic and Atmospheric Administration. Retrieved on October 28, 2002, from: Newman, Wendi & Watson, Fred (2003). Land use / Land cover of the Central Coast Region of California. The Watershed Institute, California State University Monterey Bay, Publication No. WI Ormsby, T., Napoleon, E., Burke, R., Groessl, C., & Feaster, L. (2001). Getting to Know ArcGIS Desktop, Basics of ArcView, ArcEditor, and ArcInfo. Redlands CA: ESRI Press. Planert, Michael & Williams, John S. (1995). US Geological Survey Water Atlas of the United States Segment 1 California Nevada: Salinas Valley, HA-730B. Retrieved on August 31, 2002, from: Salinas Valley Water Project: Environmental Impact Report/Environmental Impact Statement Draft, June Monterey County Water Resources Agency. Retrieved on August 31, 2002, from: Skinner, Brian J. and Porter, Stephen C. (1995). The Dynamic Earth An Introduction to Physical 31