TECHNICAL MEMORANDUM
To:
Thomas Field, RPU
Fakhri Manghi, WMWD
CC:
Ali Taghavi, WRIME
Jim Blanke, WRIME
From:
Reza Namvar
Date:
March 06, 2009
Subject:
Task 3.2 –Conceptual Model
Riverside-Arlington Basins Numerical Groundwater Model and GWMPs
Development Project
Project
Reference:
212.T03.00
INTRODUTION
The purpose of developing a conceptual model is to simplify the modeling problem and
organize the relevant field data and information so that the hydrogeologic system can be
analyzed (Anderson and Woessner, 1992). The actual hydrogeologic system is too complicated
to model and needs to be simplified as much as practicable. However, a conceptual model
should retain enough complexity and level of detail in the representation of the actual field
conditions so that the numerical model can reproduce the physical system responses with
reasonable accuracy. Simulation of the long-term regional groundwater response requires the
following:

Assessment of the hydrologic components of the physical system being modeled;

Delineation of hydrogeology;

Specification of associated land and water use that affect groundwater levels;

Description of boundary conditions; and

Definition of horizontal and vertical flow regimes within the system.
Development of a sound conceptual model is essential to understanding how the groundwater
basin may respond to different water management scenarios. The conceptual model serves as
the basis for the development of the numerical groundwater model.
MEMORANDUM OBJECTIVE
The objective of this memorandum is to describe the conceptual groundwater model of
Riverside-Arlington Basins and present the interrelationship of the various hydrogeologic and
land and water use components in the model area. The conceptual model is the basis for
development of the numerical groundwater model.
1
Task 3.2 – Conceptual Model
The objective of Task 3.2 is to develop a conceptual model for the Riverside-Arlington Basins
and a portion of the Rialto-Colton Basin. Development of the conceptual model includes
defining the following:

Model domain

Hydrostratigraphic units

Boundary conditions

Range of values of aquifer parameters (hydraulic conductivity, specific yield, and
storage coefficient)

Length of the calibration period

Regional groundwater flows

Initial conditions

Model grid size
Development of the hydrostratigraphic units and model layers was based on geologic crosssections developed by Numeric Solutions, LLC, Ventura, CA (Numeric Solutions) under
separate contract.
2
Task 3.2 – Conceptual Model
1. MODEL DOMAIN
The model area is located in the southeastern region of the Santa Ana River Watershed in
Southern California (Figure 1). The Santa Ana River enters the model area at the northeastern
boundary and exits at the western boundary.
The domain for the Riverside-Arlington Basins numerical groundwater model (RiversideArlington Model) is defined by the hydrologic and hydrogeologic setting of the model area as
defined in the following sections and with due considerations for future applications of the
numerical groundwater model. The boundaries of the Riverside-Arlington Model are primarily
based on the boundaries of the Riverside-Arlington Basin (DWR Basin No. 8-2.03) and RialtoColton Basin (DWR Basin No. 8-2.04), as defined by the DWR Bulletin 118 (California
Department of Water Resources, 2003). The Riverside-Arlington Model area covers a total area
of 95.5 square miles consisting of 23.2 square miles in the Arlington Basin, 65.3 square miles in
the Riverside Basin, and 7 square miles in the Rialto-Colton Basin.
The boundaries of the Riverside-Arlington Model consist of the groundwater divide with the
Chino Basin at the northwest boundary; the Jurupa Mountains, Pedley Hills, and other surface
topographic features at the western boundary; Arlington Narrows at the southwestern
boundary; the Box Springs Mountains at the southern and eastern boundaries; the San Jacinto
Fault at the northeastern boundary; and the Rialto-Colton Basin at the northern boundary. The
internal boundary between Arlington Basin and Riverside Basin is based on the 1969 Judgment
boundaries. The internal boundary between Riverside Basin and Rialto-Colton Basin is
represented by the Rialto-Colton Fault. Riverside Basin is divided into Riverside North and
Riverside South basins at the Riverside-San Bernardino county line. This is also the boundary
between San Bernardino Valley Municipal Water District and Western Municipal Water
District.
The Riverside-Arlington Model area is primarily an urban area with a significant agricultural
area (see Section 7. Land Use and Groundwater Recharge) and historically groundwater has
been used for irrigation purposes and municipal water supplies. Water used in the RiversideArlington Model area is pumped from wells within the model area as well as wells in Bunker
Hill Basin to the north. To meet the water demands in the Riverside-Arlington Model area, the
groundwater supplies are supplemented in dry years by imported water from Western
Municipal Water District.
The general movement of groundwater in the model area is from the northeast to the west and
southwest towards Chino Basin and Temescal Basin, respectively. The groundwater levels in
the Riverside-Arlington Model area have been dropping during the last 15 to 20 years (see
Section 5. Groudwater Levels for more details).
3
Task 3.2 – Conceptual Model
2. HYDROLOGY AND CALIBRATION PERIOD
PRECIPITATION
Rainfall data in the model area is collected by the Riverside County Flood Control and Water
Conservation District (RCFCWCD) at Station 179 and several other stations. However,
RCFCWCD uses Station 179 as the representative station for Riverside area. Station 179 is
located in the middle of the Riverside Groundwater Basin near the intersection of Highway 91
and Central Avenue (Figure 2.1). RCFCWCD suggested that data from Station 179 is reliable
and has the highest quality. Rainfall data for Station 179 was provided by RCFCWCD and
includes daily data from 1880 to 2008 with a gap from 1940 to 1948. The annual record of
rainfall and the cumulative annual departure from mean at Station 179 are shown on Figure 2.2.
The long-term average annual rainfall for 1880 to 2008 is 10.3 inches. Figure 2.3 shows the longterm average monthly rainfall at Station 179. A map displaying lines of equal rainfall (isohyets)
from California Spatial Information Library, developed from 1900-1960 data, indicates that
annual rainfall ranges from 9 to 11 inches in the Arlington and Riverside South basins.
However, the long-term average rainfall increases to approximately 14 inches in the Riverside
North and Rialto-Colton Basins.
CALIBRATION PERIOD
A thirty-two year simulation period from 1976 to 2007 will be used for calibration and
verification of the Riverside-Arlington Model. This simulation period was selected because it
includes several wet and dry periods and adequate data are available for the simulation period.
The available data include, in part, annual groundwater production by well, seasonal
groundwater elevations, daily rainfall data, daily Santa Ana River stream flow data. The
average annual rainfall for the calibration period of 76-05 period was 11.2 inches which is 0.9
inches higher than the 1880 to 2008 average annual rainfall of 10.3 inches.
SURFACE DRAINAGE AND INFILTRATION PATTERN
A map of ground surface elevations in the model area was developed based on the most recent
available US Geological Survey (USGS) Digital Elevation Map (DEM) and utilizing ArcGIS
(Figure 2.4). Elevations in Figure 2.4 range from approximately 600 feet above Mean Sea Level
(MSL) to 3,100 feet above MSL. Within the model area, ground surface elevations range from
approximately 700 feet above MSL in the Arlington Narrows and Riverside Narrows areas to
just over 1,200 feet above MSL in the northwest portion of the model area, near the Chino Basin
groundwater divide. Along the Santa Ana River, the ground surface slopes westward from
approximately 975 feet MSL in the east to approximately 710 feet MSL at the Riverside
Narrows.
4
Task 3.2 – Conceptual Model
Surface drainage and infiltration is governed largely by land use and soil type. On
undeveloped surfaces (i.e., not covered by paving or buildings) soil type is a primary factor in
runoff potential. The National Resource Conservation Service (NRCS) developed digital
mapping of the soil surveys in the model area, which are available through the USDA –NRCS
Soil Data Mart (http://soildatamart.nrcs.usda.gov). Data from these digital soil surveys,
downloaded in December 2008, are displayed on Figure 2.5. The soil types identified in the soil
survey data are associated with four hydrologic soil groups according to their runoff potential
and infiltration characteristics (Table 2.1).
Table 2.1 – Characteristics of Hydrologic Soil Groups
Soil Group
Characteristics
Group A
Sand, loamy sand or sandy loam, low runoff potential and high infiltration
rate. Primarily deep well drained soils with high sand or gravel content.
Group B
Silt loam or loam, moderate infiltration rate when thoroughly wetted.
Mostly deep to moderately deep well drained soils with moderate to low
sand content.
Group C
Sandy clay loam, low infiltration rates when thoroughly wetted. Fine to
moderately fine texture, often with layers that block downward movement
of water.
Group D
Clay loam, silty clay loam, sandy clay, silty clay or clay. Very fine texture
with high runoff potential and low infiltration rates. Often very shallow,
over bedrock or high water table.
STREAMFLOW
There are four Santa Ana River stream gaging stations within the model area. Three of the
gages are located near the intersection of Interstates 10 and 215 (in the Rialto-Colton Basin) and
one is located just downstream of the Riverside Narrows. Two of the three upstream gages are
tributary gages located in the upper reaches of the Santa Ana River on Lytle Creek and Warm
Creek. All four USGS stream gages are shown on Figure 2.1. Table 2.2 provides location and
data availability of the selected USGS stream gages.
Figure 2.6 shows the Santa Ana River inflows (sum of flows at E Street, Lytle Creek, and Warm
Creek gages) and outflows through the MWD Crossing at the Riverside Narrows. Figure 2.6
also shows the reclaimed water discharges into the Santa Ana River from the Colton and Rialto
wastewater treatment plants as well as discharges from the Rapid Infiltration Extraction (RIX)
Wastewater Treatment Facility of the Colton/San Bernardino Regional Tertiary Treatment and
Water Reclamation Authority. The average Santa Ana River inflow is less than 50,000 AFY;
however, the inflows can exceed 200,000 AFY during flood years. The total Santa Ana River
inflows are less than the total outflows at the Riverside Narrows. This is assumed to be due to
5
Task 3.2 – Conceptual Model
stream gains from rising groundwater at the Riverside Narrows area, surface water drainage
from the model area, and reclaimed water discharges.
Table 2.2 – Location and Data Availability of Selected USGS Stream Gages
Available Data
Station
No.
Stream Name
11059300
Santa Ana River
11066460
Location
Frequency
Start Date
End Date
E Street @ I-10
Daily
Mar 1939
Present
Santa Ana River
MWD Crossing @
Riverside Narrows
Daily
Mar 1970
Oct 2007
11060400
Warm Creek
Near San Bernardino
Daily
Mar 1964
Present
11065000
Lytle Creek
Colton
Daily
Oct 1957
Present
3. HYDROSTRATIGRAPHY
Preliminary hydrostratigraphy for the Riverside-Arlington Model is based on drillers’ logs
which were coded and interpolated into a three-dimensional hydrostratigraphic model by
Numeric Solutions. The objective was to group the aquifer material into discrete layers and
develop zones of similar aquifer properties for use in the model.
THREE-DIMENSIONAL HYDROSTRATIGRAPHIC MODEL OF RIVERSIDE-ARLINGTON BASINS
A three-dimensional hydrostratigraphic model (3-D Model) of the Riverside-Arlington Model
area is being developed by Numeric Solutions in coordination with WRIME and Riverside
Public Utilities (RPU) for Western Municipal Water District (WMWD). Figure 3.1 shows an
example of a cross-section from this model. Numeric Solutions based the hydrostratigraphic
model on available drillers logs, which were coded with depth based on lithology (Table 3.1).
Interpolation techniques were used to develop the 3-D Model of the model area from ground
surface to bedrock. Sixteen cross-sections, such as the one shown in Figure 3.2, will be
developed based on the 3-D Model to assist in visualization and understanding of
hydrogeologic conditions and development of model layers. The details of development of the
3-D Model and the cross-sections will be provided in Numeric Solutions’ report.
MODEL LAYERS
The unconsolidated sediments within the model area consist of River Channel Deposits along
the Santa Ana River channel, Younger Alluvium along the flood plain and below the active
6
Task 3.2 – Conceptual Model
River Channel Deposits, and Older Alluvium (GeoTrans, 2003). Preliminary review of the 3-D
Model indicates that a maximum of three model layers will be needed to capture the vertical
variability shown in the 3-D Model cross-sections of the Riverside and Rialto-Colton Basins. A
maximum of two model layers will be needed to for the Arlington Basin. The layers will be
assigned to group together, to the extent possible, areas of similar aquifer parameters. Within
the layers, zones of different aquifer parameters will be assigned to capture horizontal
variability. Aquifer parameter values will be developed with assistance from the 3-D Model
which can average over lateral and vertical variations to provide estimates of aquifer
parameters. Delineation of model layers will be finalized when the development of the 3-D
Model is complete.
Depths of the wells gradually increase from Arlington Basin in the south towards Rialto-Colton
Basin in the north. Table 3.2 on page 19 provides depth information for 88 wells in the model
area. Limited data from well clusters are available to determine the vertical gradients between
the model layers; however, water level data from nearby wells completed to different depths
will be used for model calibration.
4. AQUIFER PARAMETERS
AQUIFER PARAMETERS FROM PREVIOUS MODELS
Aquifer parameter data were reported in previous modeling efforts by Wildermuth (2008) and
GeoTrans (2003). Table 4.1 on page 23 shows the aquifer parameters data reported by
Wildermuth and GeoTrans. The Wildermuth data are concentrated in the Arlington Basin,
while the GeoTrans data are concentrated in the Riverside Basin, primarily north of Highway
60/215.
Hydraulic Conductivity
Figure 4.1 illustrates the hydraulic conductivity data used by Wildermuth and GeoTrans to
estimate the hydraulic conductivity of their models. As shown in Figure 4.1, hydraulic
conductivity is highest in the Arlington Basin, particularly at the desalter wells, with values
approaching 500 ft/day. In the Riverside Basin, values range from about 5 ft/day to almost 250
ft/day.
Specific Capacity
The specific capacity values in Table 4.1 are displayed on Figure 4.2. The highest observed
specific capacity values occur in the east-central portion of the model area. Values over 150
gpm/ft are reported in the area south of the county line and east of Main Street.
7
Task 3.2 – Conceptual Model
Specific Yield
Specific yield values are reported by Wildermuth (2008) for the Arlington Basin and portions of
the lower Riverside South Basin. Wildermuth estimated the specific yields at wells by
digitizing borehole logs and assigning specific yield values to each lithologic description using
USGS estimates (Johnson, 1967). A thickness-weighted average of specific yield was calculated
for each well borehole.
The GeoTrans model (2003) simulates the steady state conditions and does not address the
aquifer storage parameters. Figure 4.3 illustrates the distribution of specific yield in Arlington
Basin. Specific yield ranges from 0.05 to 0.19 with higher values occurring in deeper parts of
aquifer along Highway 91.
AQUIFER PARAMETERS AVAILABLE FOR RIVERSIDE-ARLINGTON MODEL
The following sources of aquifer parameter data are available for the Riverside-Arlington
Model area:

Aquifer parameter data reported by previous modeling efforts;

New aquifer tests - RPU will perform 72-hour aquifer tests in the Flume wells
area early in 2009; and
Zones of similar aquifer materials as defined by the 3-D hydrostratigraphic
model being developed by Numeric Solutions.

WRIME will analyze the above data and develop a new set of aquifer zones for aquifer
parameters. The estimated aquifer parameter zones and values will be refined during model
calibration process.
5. GROUNDWATER LEVELS
There are three major groundwater level databases available for calibration of the RiversideArlington Model. These databases were provided by the Santa Ana Watershed Project
Authority (SAWPA) and Western-San Bernardino Watermaster (Watermaster). The details of
these databases are as follows:

Cooperative Well Measuring Program Database provided by Watermaster – This
database covers the Upper Sana Ana River Watershed, San Jacinto Watershed,
and Santa Margarita Watershed. Groundwater level data are available for 1993 to
present and includes fall and spring measurements for more than 4,500 wells.

Santa Ana Basin Relational Information Network Application (SABRINA)
Database provided by SAWPA – This database covers most of the Santa Ana
River Watershed and includes 549 wells in the model area. Groundwater level
data are available for 1930s to present. Several wells have annual water levels for
the calibration period.
8
Task 3.2 – Conceptual Model
Ambient Water Quality (AWQ) Database provided by SAWPA - Similar to
SABRINA, this database covers most of the Santa Ana River Watershed and
includes 472 wells in the model area. Groundwater level data are available for
1930s to present. Several wells have annual water levels for the calibration
period.

Most wells in AWQ database are also included in SABRINA database. AWQ has been recently
used for water quality analysis of the Santa Ana River Watershed. In review of these databases,
several discrepancies were detected in AWQ and SABRINA databases. Two to three feet of
difference in recorded water levels were detected for same wells in the two databases and
discrepancies up to 10 feet were detected in a few wells. The AWQ database has been through a
more recent quality control as it is the database used to calculate Ambient Water Quality for the
triennial reports. For development of the Riverside-Arlington Model, groundwater elevations
will be obtained primarily from AWQ database and if needed from the other two databases.
Based on data provided by the SAWPA databases, groundwater level data for the model area
are available since 1945 on a semi-regular basis. Annually, an average of 150 wells have been
monitored for water levels in the Riverside Basin, 26 wells in the Arlington Basin, and 30 wells
in the portion of the Rialto-Colton Basin in the model area (Figure 5.1). Most data for 1988 to
1992 are not available electronically and are not shown in Figure 5.1. Hard copies of the missing
1988 to 1992 data are available from WMWD. Table 5.1 shows average seasonal monitoring in
the model area by basin. Duplicate data were removed from Figure 5.1 and Table 5.1.
Table 5.1 Seasonal Groundwater Monitoring – Average Number of Wells Measured
(Source: SABRINA and AWQ Databases from SAWPA)
Season
Riverside Basin
Arlington Basin
Rialto-Colton Basin
Spring
130
21
28
Fall
76
11
21
HISTORICAL GROUNDWATER LEVEL CHANGES
Historical groundwater level changes in the model area are shown in the contour maps of
Figures 5.2a and 5.2b through 5.5a 5.5b and hydrographs of Figure 5.7. The locations of the
wells for the hydrographs of Figure 5.7 are shown on Figure 5.6. These figures illustrate
seasonal groundwater levels for Spring and Fall of 1975, 1985, 1995, and 2005. Figures 5.2
through 5.5 also show the location of the wells with water level data used for generation of the
contour maps. There are more groundwater level data for spring than for fall and the spring
contour maps are developed from more data points. Groundwater levels in Spring 1965 were
approximately 950 feet above MSL in the northeast and as low as 650 feet above MSL in the
9
Task 3.2 – Conceptual Model
southwest. The pattern of higher groundwater in the northeast and lower groundwater in the
southwest, with minor variations, has remained fairly consistent throughout the last 80 years.
A contour map of historical groundwater levels in 1934, generated by Eckis(1934), and contour
maps generated by recent modeling studies by Wildermuth (2007), GeoTrans (2003), and
CH2MHill (2003) show similar magnitudes and patterns of groundwater elevation fluctuations.
Figures 5.8a and 5.8b illustrate the change in groundwater levels between 2005 and 1975 for
spring and fall, respectively. Under both spring and fall conditions, +/- 100 feet of changes in
groundwater levels from 1975 to 2005 are seen in the northeast and southwest regions. In the
southwest region, operation of desalter wells in the central Arlington Basin has significantly
lowered the groundwater levels. In the northeast area, the reduction in pumping has resulted
in higher groundwater levels.
INITIAL GROUNDWATER LEVELS
Initial groundwater levels for the Riverside-Arlington groundwater model are based on
groundwater levels of Spring 1976. The inverse distance interpolation method in ArcGIS
version 9.3 was used to develop the Spring 1976 groundwater level raster. This raster was used
to assign initial groundwater levels to active model cells.
6. BOUNDARY CONDITIONS
The boundary conditions in the model area consist of faults, groundwater divides, groundwater
flow to the adjacent basins, and recharge from small watersheds surrounding the model area.
Some of the boundary conditions are illustrated on Figure 6.1. The boundary
conditions/locations are:


Faults

San Jacinto Fault

Rialto-Colton Fault
River Boundary


No Flow Boundary




Santa Ana River
Chino Basin Groundwater Divide
Constant Head Boundary

Riverside Narrows

Hole Lake Area
General Head Boundary

Arlington Narrows

Artificial Boundary Transecting the Rialto-Colton Basin
Recharge Boundary
10
Task 3.2 – Conceptual Model

Mountain Front Recharge Along Model Boundaries from Watersheds
Surrounding the Model Area
FAULTS
The eastern-most boundary for the model area is the San Jacinto Fault Zone. The San Jacinto
Fault Zone is a series of loosely connected right lateral strike-slip fault segments that trend
northwest. Within the Fault Zone, the San Jacinto Fault separates the Bunker Hill Groundwater
Basin from the Rialto-Colton Groundwater Basin. The flow across the San Jacinto Fault will be
simulated in the model by a series of injection wells along the fault. The flow quantities will be
based on estimates prepared in Task 1 and will be adjusted during the calibration process.
To the west of the San Jacinto Fault and separating the Rialto-Colton Basin from the Riverside
Basin lies the Rialto-Colton Fault. This fault is also part of the San Jacinto Fault Zone. Recent
research suggests that the Rialto-Colton Fault actually consists of many smaller strike-slip faults
in very close proximity to each other (20-30 meters) extending across a zone nearly ½ mile wide
and trending to the northwest (Gandhok, G., 2003). The Rialto-Colton Fault acts as a
groundwater barrier between the adjoining basins, however, estimates of groundwater flow
through the fault are variable (DWR, 1970; Woolfenden and Koczot, 2001; and Woolfenden and
Kadhim, 1997). The Rialto-Colton Fault is within the model area and will be treated in the
model as a horizontal flow barrier and the flow across the Rialto-Colton Fault will be based on
estimates prepared in Task 1 and will be adjusted during calibration process.
GROUNDWATER DIVIDE
The Chino groundwater divide is located along the northwest boundary of the model area and
is defined by a ridge of bedrock that rises sharply out of the Riverside Basin (Figure 6.1). This
ridge has been inferred in many previous studies and is partially confirmed by a total lack of
groundwater production wells in the area between the Riverside and Chino Basins. The Chino
Basin Divide will be simulated as a no flow boundary.
GROUNDWATER OUTFLOW
Groundwater outflow at the boundaries of the model may occur at five locations as shown in
Figure 6.1:


Constant Head Boundary

Riverside Narrows in the west-central area

Hole Lake area to the west
General Head Boundary

Artificial boundary transecting the Rialto-Colton Basin in the north

Arlington Narrows to the west
11
Task 3.2 – Conceptual Model
Riverside Narrows - The Riverside Narrows are an area of rising groundwater where the Santa
Ana River exits the Riverside Basin in the west-central boundary of the model area. Figure 6.2
illustrates the historical groundwater levels of Mason-Old well at the Riverside Narrows. The
location of the Mason-Old well is shown in Figure 5.6. The Riverside Narrows will be treated as
a constant head boundary with groundwater elevations based on historical levels.
Hole Lake Area - Hole Lake is an area of rising groundwater near the western boundary of the
Arlington Basin, southwest of the Riverside Narrows. The ground surface in this area slopes
very gently to the north and bedrock is shallow. These factors, in combination with shallow
groundwater lead to minor seepage out of the basin to the north. This boundary will be treated
as a constant head boundary with groundwater elevations based on historical levels.
Rialto-Colton Basin Boundary - The amount of water flowing through the artificial boundary
transecting the Rialto-Colton Basin is variable and depends on pumping patterns within the
Rialto-Colton Basin. This boundary will be simulated as a general head boundary with annual
variation based based on the historical water levels and will be adjusted during calibration
process.
Arlington Narrows - The groundwater basin in the Arlington Narrows area is slightly
constricted and there is a bedrock high in this area. The amount of water flowing through the
Arlington Narrows is variable and depends on pumping patterns within the Arlington Basin
and Temescal Basin to the west. Figure 6.3 shows the historical groundwater levels of Dudley
well at the Arlington Narrows. The location of the Dudley well is shown in Figure 5.6. The
Arlington Narrows will be simulated as a general head boundary with annual variation based
on the historical groundwater levels and will be adjusted during calibration process.
SANTA ANA RIVER
The channel of the Santa Ana River, with the exception of a small concrete lined section in the
Riverside North Basin, is unlined in the model area. Streamflow is measured at three gages in
the Rialto-Colton Basin in the vicinity of the intersection of Interstates 215 and 10 and at one
gage at Riverside Narrows. Three wastewater treatment facilities have been discharging
tertiary treated wastewater to the Santa Ana River. These facilities and the period of time for
their discharges to the Santa Ana River are RIX, 1995-2009, City of Colton wastewater treatment
facility, 1970-1996, and City of Rialto wastewater treatment facility, 1970-2009. The annual
Santa Ana River flows and discharges to the river are shown in Figure 2.6. Very limited field
data are available on quantities of water exchanged between the Santa Ana River and the
aquifer. As presented in the Technical Memorandum for Task 2, in the previous modeling
efforts of the Riverside Groundwater Basin the quantities of the Santa Ana River recharge were
estimated in the model calibration process.
12
Task 3.2 – Conceptual Model
Depth to groundwater along the Santa Ana River, as shown in Figure 6.4, is greater in the
northern parts of the model area and gradually decreases towards the Riverside Narrows where
groundwater discharges into the River. The Santa Ana River will be simulated by the River
Package of MODFLOW model with the highest river recharge in the Riverside North Basin.
The river recharge will be adjusted in the calibration process.
MOUNTAIN FRONT RECHARGE
There are many small watersheds around the model area that contribute to groundwater
recharge in the model area. The small watersheds, as shown in Figure 6.5, were mapped based
on a USGS DEM and delineated by surface water divides. The runoff and groundwater
recharge from the small watersheds will be estimated in the calibration process. The mountain
front recharge will be estimated using the IDC model (see TM 3.3) and recharge values will be
assigned to the corresponding model cells along the edge of each small watershed. The
mountain front recharge will be adjusted in the calibration process. The range of mountain
front recharge estimated in the water budget tables of TM 1 will be used as reference for
adjusting the recharge rates.
7. LAND USE AND GROUNDWATER RECHARGE
Land use information in the model area was evaluated for 1993, and 2008. Land use was
classified into five groups: urban, native, agricultural, riparian, and parklands. The model area
was divided into small subregions based on 2008 land use characteristics and soil type. The
land use groups were assigned to each subregion based on land use characteristics of each
subregion. A subregion is a section of the model area with similar land use patterns and soil
type.
The 1993 model land use was developed from several sources. The initial land use was based
on DWR 1993 data. WRIME adjusted the DWR 1993 land use data by comparison to County of
Riverside 1995 land use and 2008 aerial photo. A parcel level land use map for 1993 is shown as
Figure 7.1. The land use data was then transferred to the subregions and a percent urban map
was developed (Figure 7.2).
The 2008 land use analysis was based entirely on 2008 aerial photographs and was conducted
on the subregion level only. The analysis consisted of determining the areas of urban, native,
agricultural, riparian, and parklands use of each subregion The percentages of urban areas of
the subregions are displayed in Figure 7.3.
A comparison of land use patterns between 1993 and 2008 is illustrated on Figure 7.4. It shows
the decreased agricultural land use and increased urban land use in the model area, as well as a
small decrease in riparian areas and a small increase in parklands.
13
Task 3.2 – Conceptual Model
Groundwater recharge will be calculated for each subregion as part of the model calibration.
The Soil Moisture Routing Model, developed by California Department of Water Resources
(2007), will be used for groundwater recharge calculations. This model is described in TM 3.3.
8. WATER SUPPLY AND DEMAND
The objective of this section is to describe the components of the water supply and demand in
the Riverside-Arlington Model area. This information will be used for estimating groundwater
recharge from applied water.
GROUNDWATER PRODUCTION
Groundwater production in the model area was analyzed using data received from the San
Bernardino-WMWD Watermaster. Figures 8.1 through 8.5 illustrate groundwater production
volumes on average and for 1975, 1985, 1995, and 2005 respectively. Figure 8.6 shows the total
annual groundwater production from the wells in the model area for 1947 to 2007 period.
RPU also produces groundwater from its wells in the Bunker Hill Basin which is delivered to its
service area in Arlington and Riverside Basins. During 1999-2003 period, RPU pumped
approximately 66,000 acre-feet/year from the Bunker Hill Basin, 9,500 acre-feet/year from the
Riverside North Basin, and 19,500 acre-feet/year from the Riverside South Basin.
IMPORTED WATER
RPU purchases small quantities of treated imported water from WMWD to meet peak demand
needs in the RPU service area. The water purchased from WMWD is State Water Project water
that has been imported through the Metropolitan Water District (MWD) and treated at the Mills
Treatment Plant (City of Riverside, 2005). The RPU contract with WMWD allows for water
delivery into the PRU service area through either the Mills Connection 24-C or the Van Buren
Highline. Historically, these connections have provided up to 5,493 acre-feet (1990) and 4,986
acre-feet (1999) respectively.
RECYCLED WATER USE
Currently, the City of Riverside operates a small network of 8-inch and 12-inch distribution
mains to transport recycled water from the Riverside Regional Water Quality Control Plant
(RRWQCP) to the Van Buren Golf Course, Van Buren Urban Forest, and Toro Manufacturing
Company. Additionally, there are existing, but currently unused, recycled water mains along
Van Buren Boulevard and Doolittle Avenue.
Treated effluent from the RRWQCP that is not utilized through the recycled water program is
discharged into the Santa Ana River at Riverside Narrows downstream from the model area.
The current effluent release to the Santa Ana River is approximately 36,000 AFY and serves to
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Task 3.2 – Conceptual Model
satisfy downstream judgment requirements in relation to the City of Riverside’s water use
permits.
AGRICULTURAL WATER USE
Agricultural water use has decreased from approximately 64,000 AFY in 1969 to approximately
14,000 AFY in 2007. Based on information from USGS (Scott, 1977), agricultural water use in
1969 accounted for 60% of all water use in the Riverside Basin. Based on data from RPU the
agricultural water use accounted for about 19% of water consumption in 1985. This trend is the
inverse of the urbanization trend in the model area over the last 50 years. A linear trend of
decrease in agricultural water use was assumed for the period from 1969 to 1984 (Figure 8.7).
URBAN WATER USE
Urban water use in the model area has increased by almost 100% since 1965, from an estimated
rate of 55,000 AFY in 1969 to an estimated rate of 108,000 AFY in 2007. This increase in water
use has mirrored the increase in urban development in the Riverside and Arlington Basins.
Urban water use in the RPU service area from 1985 to 2007 is based on data reported by the
RPU, while urban use in the RPU service area from 1976 to 1984 was estimated based on 1985 to
2007 data (Figure 8.7). It was assumed that the urban water use in the model area is correlated
with groundwater production in the model area. It was also assumed that the correlation of
groundwater pumping and water use from 1976 to 1984 is similar to the correlation for the
period from 1985 to 2007. The correlation ratio of groundwater pumping and water use of 1985
to 2007 period was multiplied by annual groundwater pumping of 1976 to 1984 to estimate the
annual water use of 1976 to 1984 period.
It was assumed that, in the model area, the rate of urban water use outside the RPU service area
is the same as the rate of water use inside the RPU service area. The water use inside the model
but outside the RPU service area was estimated by multiplying the rate of water used in the
RPU service area by the urban areas outside the RPU service area.
9. MODEL GRID RESOLUTION
A uniform resolution grid represents the most accurate form of the finite difference solution.
MODFLOW model allows using a variable grid resolution with finer resolution at areas of
interest to achieve higher accuracy. As is the nature of the finite difference grids, refinement in
one area of the grid will extend to other areas of the grid, increasing the number of model rows
and columns.
Currently, the areas of future projects of interest for the Riverside-Arlington Model include the
desalter wells in Arlington Basin, future desalter wells in Riverside South Basin, groundwater
production from wells in the vicinity of the Santa Ana River, and proposed recharge operations
15
Task 3.2 – Conceptual Model
at the Riverside North Basin and the Arlington Basin. A list of projects of interest is presented
in Technical Memorandum 3.1, Modeling Project Objectives. Refinement of model grid in these
areas would extend to almost all other areas of the Riverside-Arlington Model grid. Thus, a
uniformly fine preliminary grid is suggested for the Riverside-Arlington Model. Each cell will
have a dimension of 50 x 50 meters (164 x 164 feet). This is similar to the grid of the Arlington
Model (Wildermuth, 2008), finer than other previous models (GeoTrans, 2003, CH2M Hill,
2003), and is expected to be adequate for simulation of the future projects of interest. Figure 9.1
shows the preliminary uniform grid with 50 x 50 meter cell size covering all of the conceptual
model area. The final grid coverage area will be slightly smaller than the conceptual model as
some of the model cells close to the boundaries and with higher bedrock elevations may not
have adequate saturated thickness and become dry during the calibration. If the computation
time of the Riverside-Arlington Model with this fine grid is found to be excessive, then a grid
which is coarser in the areas away from the proposed project areas will be used. The final grid
coverage area and the cell size will be determined in the calibration process.
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Task 3.2 – Conceptual Model
REFERENCES
Anderson, M.P. and W.W. Woessner, 1992. Applied Groundwater Modeling: Simulation of Flow and
Advective Transport, Academic Press, Inc., New York, 381 pp.
California Department of Water Resources, 1970. Meeting water demands in the Chino-Riverside
area. Bulletin No. 104-3, 27 p.
California Department of Water Resources, 2003. California’s Groundwater – Bulletin 118 Update
2003.
California Department of Water Resources, 2007. Soil Moisture Routing and Agricultural Demand
Computation in IWFM Demand Calculator (IDC v1.0). Prepared by Emin Can Dogrul, Hydrology
Development Unit, Modeling Support Branch, Bay-Delta Office.
CH2MHill, 2003. Update of the Groundwater Flow Model and Assessment of Operational Performance
Criteria for the RIX Facility. Prepared for Colton/San Bernardino Regional Tertiary Treatment
and Water Reclamation Authority.
City of Riverside, 2005. Urban Water Management Plan. City of Riverside.
Dorsey, R.J., 2002, Stratigraphic Record of Pleistocene Initiation and slip on the Coyote Creek Fault,
Lower Coyote Creek, Southern California. In: Barth, A. (ed.) Contributions to Crustal Evaluation of
the Southwest United States, Boulder, CO, GSA Special Paper, 365pp, p.251-264.
Eckis, Rollin, 1934. Geology and Ground Water Storage Capacity of Valley Fill. California
Department of Public Works, Division of Water Resources, South Coastal Basin Investigation,
Bulletin No. 45
Gandhok, G., et. al. 2003, Shallow Geometry and Velocities along the Rialto-Colton Fault, San
Bernardino Basin, California. American Geophysical Union, Fall Meeting 2003, Abstract # S21F0393
GeoTrans, 2003. Riverside Groundwater Basin Study Report, Project Agreement 16 – Phase 2.
Prepared for the Santa Ana Watershed Project Authority and the City of Riverside Public
Utilities Department, Water Division.
Johnson, A.I., 1967. Specific yield—compilation of specific yield for various materials: U.S. Geological
Survey, Water Supply Paper 1662-D, 74 p.
Scott, M.B., 1977. Development of Water Facilities in the Santa Ana River Basin, California, 1810-1969,
USGS OFR 77-398, 246pp.
Wildermuth, 2008. Feasibility Study for the Expansion of the Arlington Desalter System – Task 1
Report: Arlington Basin Groundwater Flow Model. Prepared for Western Municipal Water District.
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Task 3.2 – Conceptual Model
Woolfenden, L. and D. Kadhim, 1997. Geohydrology and water chemistry in the Rialto-Colton Basin,
San Bernardino County, California. Water Resources Investigations Report 97-4012, 101 p.
Prepared in Cooperation with the San Bernardino Valley Municipal Water District.
Woolfenden, L. and K. Koczot. 2001. Numerical Simulation of Ground-Water Flow and Assessment of
the Effects of Artificial Recharge in the Rialto-Colton Basin, San Bernardino County, California, USGS
Water-Resources Investigation Report 00-4243. Prepared in Cooperation with the San
Bernardino Valley Municipal Water District.
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Task 3.2 – Conceptual Model