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

Table of contents 1 ABSTRACT........................................................................................................................... 3 2 INTRODUCTION................................................................................................................. 4

2.1 Groundwater ................................................................................................................... 4 2.2 The Salinas Valley .......................................................................................................... 4 2.3 Seawater Intrusion .......................................................................................................... 5

2.3.1 Salinas Valley Water Project .................................................................................. 7 2.3.2 Historical Benefits Analysis .................................................................................... 7

2.4 Water Table Visualization .............................................................................................. 7 3 HYDROGEOLOGY OF THE SALINAS VALLEY......................................................... 8

3.1 SVIGSM inputs/model construction............................................................................. 10 3.1.1 Model Inputs and Aquifer Properties: .................................................................. 10 3.1.2 Model Calibration and Validity ............................................................................ 11

4 METHODS .......................................................................................................................... 12 4.1 Data Collection ............................................................................................................. 12 4.2 Data Analysis ................................................................................................................ 13

4.2.1 Animation 1: Monterey Bay to Forebay Sub-area................................................ 13 4.2.2 Animations 2: Upper Valley Sub-area .................................................................. 14 4.2.3 Animations 3 and 4: Defined Contours ................................................................ 14 4.2.4 Land use ................................................................................................................ 14 4.2.5 MPEG 4 Animation Formatting............................................................................ 15

5 RESULTS ............................................................................................................................ 15 5.1 Animation 1: Monterey Bay to Forebay Sub-area........................................................ 15 5.2 Animation 2: Upper Valley Sub-area ........................................................................... 16 5.3 Animation 3: Defined Contours 1949 – 1956............................................................... 17 5.4 Animation 4: Defined Contours 1980 – 1994............................................................... 17 5.5 Land Use ....................................................................................................................... 18

6 DISCUSSION ...................................................................................................................... 19 6.1 Animation 1 .................................................................................................................. 19 6.2 Animation 2 .................................................................................................................. 20 6.3 Climate.......................................................................................................................... 20 6.4 Animation 3 .................................................................................................................. 22 6.5 Animation 4 .................................................................................................................. 23 6.6 Land Use ....................................................................................................................... 24 6.7 Seawater Intrusion and the Salinas Valley Water Project: ........................................... 26 6.8 Other Management Uses............................................................................................... 27 6.9 Possible errors in study ................................................................................................. 28

7 CONCLUSION ................................................................................................................... 29 8 ACKNOWLEDGEMENTS ............................................................................................... 30 9 LITERATURE CITED ...................................................................................................... 30 10 APPENDIX.......................................................................................................................... 32

2

“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 1994. The animation shows the changes the Salinas Valley water table has undergone from the years 1949 through 1994. Four animations were created from these maps. Animation 1 includes the Monterey Bay to the Forebay sub-area, and is mapped from 1949 through 1994. Animation 2 shows the Upper Valley sub-area only, mapped from 1949 through 1994. 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 1994. 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 1983. 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

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

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

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 well-

abandonment. 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

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).

2.3.2 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 1949 – 1994.

2.4 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 1930 – 1999, 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

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

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 12-40 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

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).

3.1.1 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 113-3. 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

(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).

3.1.2 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

Sub-area Accuracy % Of Time

± 5ft 38% Pressure ± 10ft 70% ± 5ft 30%

East-Side ± 10ft 57%

± 5ft 55% Forebay

± 10ft 80%

± 5ft 50% Upper Valley

± 10ft 80%

4 METHODS

4.1 Data Collection

The output wa

Water Model (SVIGS

County Water Resour

from the 1,726 nodes

years, October to Sep

for all groundwater aq

mean sea level. In ad

Agency provided GIS

boundary, model grid

Precipitation d

Center, a climate data

Association. Total mo

Monterey County, wa

GIS shapefiles

obtained from the ESR

boundaries of Monter

rivers within Californ

US Geological Survey

Table 3.1: Summary of SVIGSM water table elevations, compared with real well data, 1969 through 1994 (Source: Montgomery Watson, 1997)

ter table elevations from the Salinas Valley Integrated Ground and Surface

M) were used to construct the maps for the animations. The Monterey

ces Agency prepared a file containing groundwater table elevations derived

of the SVIGSM. The groundwater elevations were averaged (by water

tember) to yearly values from the years 1949 through 1994, and averaged

uifers within the Salinas Valley basin. All elevations were adjusted to

dition to the groundwater levels, the Monterey County Water Resources

shapefiles of the hydrologic sub-areas of the Salinas Valley, basin

, and node locations within the valley.

ata for the Salinas Valley were obtained from the National Climatic Data

archive available online through the National Oceanic and Atmospheric

nthly precipitation (in inches) under California Region 4, which includes

s collected for the years 1948 through 1994 (NCDC, 2003).

of California Counties and California major roads and freeways were

I Data & Maps (1998), available with ArcView 3.2, to define the

ey County. A shapefile outlining of the State of California, and major

ia was obtained from Geography Network online, originally created by the

(2002).

12

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

4.2.1 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 sub-

area) 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 1992.

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

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 one-

second intervals, creating the animation of the Salinas Valley water table elevation from the

Monterey Bay to the Forebay sub-area.

4.2.2 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 (1949 – 1994) 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.

4.2.3 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 4.

4.2.4 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

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.

4.2.5 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

1994. The animation file can be viewed at the website

http://home.csumb.edu/s/smithdouglas/world/Doug/html/salinas_water_table.html.

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 1992. 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

Yearly Minimum Values: Animations 1,3,4

-80

-70

-60

-50

-40

-30

-20

-10

0W

ater

Tab

le L

evel

s fe

et a

bove

sea

leve

l

Figure 5.1: Minimu

5.2 Animation 2:

Animation 2

area. As with Anim

file can be viewed a

http://home.csumb.e

minimum water tab

animation and graph

table elevations dec

of depression shown

north end of the sub

Nacimiento (1956)

m water table e

Upper Vall

shows the

ation 1, are

t

du/s/smithd

le values fo

show a slo

rease from 1

in this ani

-area.

San Antonio (1967)

levation simulated by SVIGSM by year, from the Monterey Bay to Forebay sub-area

ey Sub-area

changing groundwater table elevation for the Upper Valley Sub-

as of dark red show lower water table elevation. The animation

ouglas/world/Doug/html/salinas_water_table.html. The graph of

r the Upper Valley Sub-area is shown in Figure 5.2. Both the

w overall increase in elevations from 1950 through 1967. Water

987 through 1992 and increase through 1994. There is no cone

mation, though lower water table elevations are present at the

16

Yearly Minimum Values: Animations 2

170

180

190

200

210

220

230W

ater

Tab

le E

leva

tion

feet

abo

ve s

ea le

vel

San Antonio (1967)

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 1949 – 1956

Animation 3 shows a closer look at the groundwater table elevations in the lower Salinas

Valley and coastal areas for the years 1949 through 1957. The animation file can be viewed at

the website http://home.csumb.edu/s/smithdouglas/world/Doug/html/salinas_water_table.html.

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 1980 – 1994

Animation 4 shows a closer look at the groundwater elevations in the lower Salinas

Valley and coastal areas for the years 1980 through 1994. The animation file can be viewed at

http://home.csumb.edu/s/smithdouglas/world/Doug/html/salinas_water_table.html. 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 1992.

17

5.5 Land Use

The comparison of the 1994 water table level to land use in the Salinas Valley is shown

in Figure 5.3.

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

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 1994. 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 6.1. 1992 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 1957. In 1958 there is an

increase in water table elevation. This may correspond to the construction and operation of the

19

Nacimiento Reservoir in 1957. Water table elevations continue to decline again until 1962, after

which they increase variably until 1969. 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 1981. Elevations increase

until 1983, and then generally decline until 1994.

6.2 Animation 2

Animation 2 shows the changing groundwater table elevation for the Upper Valley sub-

area 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. 1950 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 1994. 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 6.2.

20

Minimum Water Table Elevation and Precipitation (Animation 1)

1949

1950

1952

1953

1954

19941993

1991

19901989

1988

1987

19861985

1984

1983

1982

19811980

1979

1978

1977

1976

1975

1974

1973

1972

1971

19701969

19681967

1966

1965

19641963

1961

1960

1959

1958

1956 1957

1955

1951

0

5

10

15

20

25

30

35

40

45A

nnua

l Pre

cipi

tatio

n in

ches

-60

-50

-40

-30

-20

-10

0

er T

able

Ele

vatio

n fe

et a

bove

sea

leve

lPrecipForebay

Figure 6.

Figu

5.1. When c

declining tre

time period,

1962, minim

patterns thro

similar amou

increasing, a

patterns with

A sim

the total ann

minimum w

Figure 6.3 sh

table. There

occurring. T

reservoirs, a

show is that

Nacimiento (1956)

2: Minimum water ta

re 6.2 shows the

omparing the m

nds are better s

but the average

um water table

ugh the same ti

nts). This is d

nd water table

precipitation a

ilar compariso

ual precipitatio

ater table eleva

ows that the U

is little fluctua

he Upper Valle

t Nacimiento R

the releases int

San Antonio (1967)

19921962

-80

-70

Wat

ble elevation from Animation 1 compared with total annual precipitation from 1949 through 1994.

overall decreasing water table elevation, as described under Figure

inimum water table elevation with total annual precipitation, the

hown. The precipitation data for the time period varies through the

remains relatively constant. Between the years of 1949 through

elevation of Animation 1 decreases substantially. The precipitation

me period remain relatively constant (increases and decreases by

irectly visible for the year 1961 through 1962, where precipitation is

levels are decreasing. The years 1963 through 1980 show similar

nd minimum water table elevation.

n is made with minimum values from Animation 2 (Figure 5.2) and

n. The comparison is shown in Figure 6.3. The patterns of the

tion in Animation 2 roughly correspond to changes in precipitation.

pper Valley sub-area is relatively stable in terms of the groundwater

tion of the water table over time, with changes in precipitation

y sub-area receives maximum benefit from the operation of the two

iver and the San Antonio River. What this graph and Animation 2

o the Salinas River from the two reservoirs are successful in

21

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.

Minimum Water Table Elevation and Precipitation (Animation 2)

19941993

1992

1991

19901989

198819871986

1985

19841983

19821981

1980

197919781977

19761975

197419731972

197119701969

1968

1967

19661964

19651963

1962

1961

19601959

1958

1957

1956

1955

19541953

1952

19511950

1949

0

5

10

15

20

25

30

35

40

45

Ann

ual P

reci

pita

tion

inch

es

170

180

190

200

210

220

230

Wat

er T

able

Ele

vatio

n fe

et a

bove

sea

leve

lPrecipUpper Valley

San Antonio (1967)

Nacimiento (1956)

Figure 6.3: Minimum water table elevation from Animation 2 compared with total annual precipitation from 1949 through 1994.

6.4 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

T

seawater

where se

6.5 An

U

moveme

depressi

example

Figure 6.4: Map of 1957 groundwater table elevations from Animation 3. Position of sea level withinthe groundwater table is drawn in black.

he use of sea level for drawing the contour line is linked to seawater intrusion. Since

intrusion occurs in coastal aquifers when the water table falls below sea level, locating

a level is in the water table is useful for predicting where problems can occur.

imation 4

sing the color break of 10-feet below sea level for Animation 4 not only shows the

nt of the groundwater table below sea level, but the reversing gradient from the cone of

on (west to east) east of the city of Salinas to the Monterey Bay (east to west). An

of this is shown in Figure 6.5.

23

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 2003. 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

land use, in addition to urban land use, increase the amount of groundwater withdrawals in the

basin.

1994 Water Table Elevation

10-foot contour intervals, from 60 feet to 20 feet below sea level

–40

–20

are

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 sub-

a mainly consists of grassland vegetation, with crops and vineyards in the northern Upper

25

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.

6.7 Seawater Intrusion and the Salinas Valley Water Project: Figure 6.7. Land use in the Upper Valley Sub-area.

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

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

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 semi-

confined 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

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

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 1987-1992.” Retrieved on October 23, 2002, from:

http://watersupplyconditions.water.ca.gov/pdf/Drought_Rpt_Chp1.pdf

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:

http://www.mclw.org/pages/publications02/roomenough/roomenough.pdf

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, 79-102.

Mills, T., Hoekstra, P., Blohm, M., & Evans, L. (1988). “Time domain electromagnetic

30

soundings for mapping sea-water intrusion in Monterey County, California.” Ground

Water, 26(6), 771-782.

Monterey County (2001). “Monterey County Draft General Plan Executive Summary, 21st

Century General Plan Update.” Retrieved October 1, 2002, from:

http://www.co.monterey.ca.us/gpu/Reports/Draft%20General%20Plan.htm

Monterey County Water Resources Agency (2001). “Seawater Intrusion in the Pressure 180-Foot

Aquifer.” 2001 Water Quality Data. Retrieved on February 13, 2003, from:

http://www.mcwra.co.monterey.ca.us/

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), 649-659.

National Climate Data Center (“NCDC”), (2002). “Average Monthly Precipitation Data,

Division 04.” National Oceanographic and Atmospheric Administration. Retrieved on

October 28, 2002, from:

http://lwf.ncdc.noaa.gov/oa/climate/onlineprod/drought/xmgrg2.html

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-2003-04.

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: http://ca.water.usgs.gov/groundwater/gwatlas/coastal/salinas.html

Salinas Valley Water Project: Environmental Impact Report/Environmental Impact Statement

Draft, June 2001. Monterey County Water Resources Agency. Retrieved on August 31,

2002, from: http://www.co.monterey.ca.us/mcwra/deir_svwp_2001/INDEX.HTM

Skinner, Brian J. and Porter, Stephen C. (1995). The Dynamic Earth An Introduction to Physical

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Geology. 3rd edition. New York: John Wiley & Sons.

Stamos, C.L., Martin, P., Nishikawa, T., & Cox, B.F. (2001). “Simulation of Ground-Water

Flow in the Mojave River Basin, California.” US Geological Survey, Water Resources

Investigations Report 01-4002 Version 3.

US Census Bureau (“USCB”), (2001). State and County Quickfacts: Monterey County,

California. United States Census Bureau. Retrieved on October 1, 2002, from:

http://quickfacts.census.gov/qfd/states/06/06053.html.

US Geological Survey (“USGS”), (2002). “State Boundaries of the United States.” Retrieved on

March 31, 2003, from: http://nationalatlas.gov/atlasftp.html

US Geological Survey (“USGS”), (2003). “Streams and Waterbodies of the United States.”

Retrieved on March 31, 2003, from: http://nationalatlas.gov/atlasftp.html

US Geological Survey (“USGS”), (2002). Calendar Year Streamflow Statistics for California;

USGS 11152500 Salinas R NR Spreckels CA. Retrieved on October 1, 2002, from:

http://waterdata.usgs.gov/ca/nwis/annual/?site_no=11152500&agency_cd=USGS

Viessman, Warren Jr. & Lewis, Gary L. (1995). Introduction to Hydrology. Fourth edition.

Boston: Addison-Wesley Longman.

10 APPENDIX

SVIGSM Calibration Wells: Sample graphs for each sub-area and aquifer layer.

All animations can be viewed at the following website:

http://home.csumb.edu/s/smithdouglas/world/Doug/html/salinas_water_table.html.

32

Pressure Sub-area: Selected Calibration Well Graphs

(Please note: Y-axis ranges are different for each graph)

33

East-Side Sub-area: Selected Calibration Well Graphs

(Please note: Y-axis ranges are different for each graph)

34

Forebay Sub-area: Selected Calibration Well Graphs (Please note: Y-axis ranges are different for each graph)

35

Upper Valley Sub-area: Selected Calibration Well Graphs (Please note: Y-axis ranges are different for each graph)

36