Appendix Part 3. 193

Appendix Part 3. Development of Groundwater 

Flow Models

Figures

A3–1. Map showing geographic extent, surficial geology, observation wells, proposed 

withdrawal sites, simulated boundary conditions, and outflow points from HSPF 

subbasins for the lower Wood River model area in the Pawcatuck River Basin, 

southwestern Rhode Island ....................................................................................................196

A3–2. Map showing model extent and boundary conditions used in the eastern Pawcatuck 

River model area in the Pawcatuck River Basin, southwestern Rhode Island..............197

A3–3. Representative cross section showing hydraulic-conductivity distribution and aquifer 

thickness in the lower Wood River model area in the Pawcatuck River Basin, 

southwestern Rhode Island ....................................................................................................198

A3–4A. Graph showing comparison of measured and model-calculated groundwater levels 

for well RIW–417 in the eastern Pawcatuck River model area in the Pawcatuck River 

Basin, southwestern Rhode Island........................................................................................207

A3–4B. Graph showing comparison of measured and model-calculated water levels for 

well SNW–006 in the eastern Pawcatuck River model area in the Pawcatuck River 

Basin, southwestern Rhode Island........................................................................................208

A3–4C. Graph showing comparison of measured and model-calculated water levels for 

well EXW–554 in the lower Wood River model area in the Pawcatuck River Basin, 

southwestern Rhode Island ....................................................................................................209

A3–4D. Graph showing comparison of measured and model-calculated water levels for 

well RIW–785 in the lower Wood River model area in the Pawcatuck River Basin, 

southwestern Rhode Island ....................................................................................................210

A3–5A. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet QUEN4 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................211

A3–5B. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet QUEN6 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................212

A3–5C. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet QUEN7 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................213

A3–5D. Graph showing comparison of measured and model-calculated baseflows for RCHRES 

outlet CHIP1 in the eastern Pawcatuck River model area in the Pawcatuck River Basin, 

southwestern Rhode Island ....................................................................................................214

A3–5E. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet CHIP2 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................215

A3–5F. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet CHIC2 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................216

A3–5G. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet PAWC3 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................217
194 Appendix Part 3. Development of Groundwater Flow Models

Tables

A3–1. Hydraulic conductivity values of the lithologic units simulated in the groundwaterflow models in the Pawcatuck River Basin, southwestern Rhode Island.......................201

A3–2. Model-calculated and measured groundwater levels in the lower Wood River 

model area in the Pawcatuck River Basin, southwestern Rhode Island........................204

A3–3. Model-calculated and measured groundwater levels in the Eastern Pawcatuck River 

model area in the Pawcatuck River Basin, southwestern Rhode Island........................206

A3–5H. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet BEAV3 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................218

A3–5I. Graph showing comparison of measured and model-calculated baseflows for HSPF 

subbasin outlet TANE1 in the eastern Pawcatuck River model area in the Pawcatuck 

River Basin, southwestern Rhode Island..............................................................................219
Spatial Discretization 195

Development of Groundwater-Flow Models

Numerical flow models are useful tools for testing and 

improving conceptual models of groundwater-flow systems 

by providing a means to synthesize existing hydrogeologic 

information into an internally consistent mathematical 

representation of a real system or process (Konikow and 

Reilly, 1999). Groundwater-flow models were developed 

for two areas within the Pawcatuck River Basin, the lower 

Wood River and eastern Pawcatuck River areas (figs. A3–1, 

A3–2). These numerical flow models were based on the 

USGS computer program MODFLOW (Harbaugh and 

others, 2000) and were used for the purposes of assessing 

the potential effects of groundwater pumping from irrigation 

and water-supply withdrawal sites proposed within the study 

area on streamflows and water levels. Results calculated 

by MODFLOW were compared to results calculated by 

the analytical streamflow depletion algorithm in the HSPF 

model and used to evaluate alternatives for the conjunctive 

management of the groundwater and surface-water resources 

in selected areas of the basin.

Model Discretization and Boundaries

The finite-difference model grid consists of a series of 

orthogonal model cells used to vary user-specified hydraulic 

parameters, model stresses, and boundary conditions spatially. 

The conceptualization of how and where water enters, moves 

through, and leaves the aquifer is critical to the development 

of an accurate flow model (Reilly, 2001). A detailed discussion of grid discretization, boundary conditions, and the use 

of finite-difference equations to simulate groundwater flow is 

presented in McDonald and Harbaugh (1988), Reilly (2001), 

and Reilly and Harbaugh (2004). 

Spatial Discretization

The total active modeled area in the lower Wood River 

subbasin is about 18 mi2, and the active modeled area of 

the eastern Pawcatuck River subbasin is about 114 mi2

(figs. A3–1, A3–2). The finite-difference grids representing these two areas consist of 290 rows and 290 columns of 

uniformly spaced model cells that are 100 ft on a side for the 

lower Wood River model and 400 rows and 210 columns of 

uniformly spaced model cells that are 250 ft on a side for the 

eastern Pawcatuck River model. Both modeled areas were 

subdivided vertically into four layers of different thicknesses 

that extend from the water table downward to encompass the 

upper 50 ft of bedrock. The eastern Pawcatuck River model 

extends from the Pawcatuck River Basin to the southern coastline of Rhode Island to represent groundwater flow better in 

the southern part of the basin.

Most previous groundwater modeling investigations of 

areas that include upland till and bedrock surrounding glacial 

stratified deposits did not explicitly simulate the upland areas, 

but rather specified the recharge that would have entered the 

aquifer through these areas as enhanced recharge at the contact 

between till and glacial stratified deposits (Dickerman and 

others, 1997; Barlow and Dickerman, 2001; DeSimone and 

others, 2002; Granato and others, 2003; Friesz, 2004). This 

approach was used to prevent numerical instabilities that often 

result from simulating steeply sloping, thinly saturated deposits, such as the upland till areas throughout the northern part of 

the Pawcatuck River Basin and discussed previously in Part 1.

A more recent investigation of the South Coastal Basin of 

southern Rhode Island (Masterson and others, 2007) included 

a fixed-transmissivity approach that allowed for the simulation of both the glacial stratified deposits and the upland till 

and bedrock areas. This approach is equivalent to simulating 

a confined aquifer, which, for steady-state conditions that 

do not represent seasonal fluctuations of the water table, is a 

reasonable representation of both areas within the aquifer. The 

benefit of this approach is that it allows for a more realistic 

representation of flow from these upland areas to the surrounding glacial stratified deposits. 

The model layer most affected by this fixed-transmissivity approach is the top layer. In the variable-transmissivity 

approach, the top of layer 1 is the water table calculated by the 

model, whereas in the fixed-transmissivity approach, the top 

of the layer must be specified. The top of the uppermost layer 

(layer 1) was initially set to the land-surface altitude, which 

was interpolated from 30-m digital-elevation-model data 

(P.A. Steeves, U.S. Geological Survey, written commun., 

2004) and then reset to the altitude of the simulated water 

table during the model-calibration process. After several 

iterations of resetting the top of layer 1 to the altitude of the 

model-calculated water table, a reasonably close match to the 

observed water-level data was achieved, and that water-table 

altitude was then specified as the top of layer 1. 

The glacial stratified deposits were then represented in 

three model layers of varying thicknesses (layers 1–3) from 

the water table to bedrock to allow for the detail necessary 

to represent the streambed thickness, vertical changes in the 

lithology, and the screened intervals of pumping wells 

(fig. A3–3). The top layer (layer 1) is relatively thin (generally 

less than 5 ft thick) to provide as realistic a representation as 

Appendix Part 3. Development of Groundwater Flow Models

By John P. Masterson
196 Appendix Part 3. Development of Groundwater Flow Models

Wood River

Meadow Brook

Diamond Brook

Wood

River Pawcatuck River

Pawcatuck River

0 0.5

1 KILOMETER

1 MILE

0 0.5

Base from U.S. Geological Survey digital data, 1:24,000,

Rhode Island stateplane projection. 1983 North American datum

RIW-458

RIW-550

RIW-481A

MW-9

RIW-785

RIW-458A

RIW-458B

Diamond Bog

Chariho

WOOD5

WOOD6

PAWC4

MEAD2

71°44' 71°42'

41°28'

41°26'

EXPLANATION

Surficial geologic deposits

Simulated model boundary conditions

Till deposits

Sand and gravel deposits

Pond

Wetland

Specified flow

Specified flux

Inactive area of model

Head-dependent flux

Observation well and identifier

Proposed pumping well 

 and identifier

HSPF subbasin outlet

 and identifier

RIW-550

RIW-785

WOOD6

X X ́ Line of cross-section 

shown in fig. A3–3

1 290

290 1

COLUMNS

ROWS

Figure A3–1. Geographic extent, surficial geology, observation wells, proposed withdrawal sites, simulated boundary 

conditions, and outflow points from HSPF subbasins for the lower Wood River model area in the Pawcatuck River Basin, 

southwestern Rhode Island.
Spatial Discretization 197

71°38' 71°32'

41°28'

41°36'

Chipuxet River

Beaver River

Usquepaug River

Queen River

Worden Pond

Pawcatuck River Taney Brook

Chipuxet River

Beaver River

Usquepaug River

Queen River

Pasquiset Brook

Worden Pond

Pawcatuck River Taney Brook

Base from U.S. Geological Survey digital data, 1:24,000,

Rhode Island stateplane projection. 1983 North American datum

0

0 1

1 2 MILES

2 KILOMETERS

1 230

400 1

COLUMNS

ROWS

BEAV3

TANE1

QUEN4

QUEN6

CHIP2

CHIC2

CHIP1

QUEN7

SNW-006

EXW-554

RIW-417

PAWC3

EXPLANATION

Surficial geologic deposits

Simulated model boundaries

Till deposits

Sand and gravel deposits

Moraine deposits

Pond

Wetland

Specified flow

Inactive area of model

Head dependent flux

Constant head boundary

Pumped well

Observation well

 and identifier

HSPF subbasin outlet

 and identifier

BEAV3

RIW-417

Figure A3–2. Model extent and boundary conditions used in the eastern Pawcatuck River model area in the 

Pawcatuck River Basin, southwestern Rhode Island.
198 Appendix Part 3. Development of Groundwater Flow Models X X’ West East 350 300 250 200 150 10050 0 -150 -200 -250 -300 -50 -100

ALTITUDE, IN FEET RELATIVE TO NGVD 29

Horizontal hydraulic conductivity values, in feet per day, and lithologic description of layer

 EXPLANATION

5,000–water

Vertical scale greatly exaggeratedSee appendix 3, figure 1 for map view

1 to 5–till1–bedrockInactive

150–coarse sand and gravel10–fine sand and gravel

ROW 152

0 0.5

1 KILOMETER

1 MILE

0 0.5

Figure A3–3. Hydraulic-conductivity distribution and aquifer thickness in the lower Wood River model area in the Pawcatuck River Basin, southwestern Rhode Island.(Location of cross section shown in figure A3–1.)
Hydrologic Boundaries 199

possible of the rivers in the modeled areas (blue cells within 

layer 1 in figure A3–3). Layer 2 generally represents the 

coarser glacial stratified deposits of sand and gravel (green 

cells), and layer 3 represents the finer glacial stratified deposits 

of silt and clay (purple cells). The bottom layer (layer 4); 

shown as gray cells (fig. A3–3), extends from the top of the 

bedrock surface to 50 ft below the bedrock surface to allow for 

flow in fractured bedrock in areas where the unconsolidated 

deposits are thin, such as beneath the upland tills (shown as 

orange cells). An example of the model layering used in this 

investigation is shown for section X-X′ (fig. A3–3) for the 

lower Wood River model (fig. A3–1).

Hydrologic Boundaries

The hydrologic boundaries in a flow model are the areas 

in which and the method by which all of the water entering 

and leaving the model is specified, and generally coincide with 

the physical boundaries of the flow system. 

In developing the model for the Pawcatuck River Basin, 

it was assumed that the groundwater and surface-water 

divides were coincident in the upland till areas and therefore 

defined the extents of the active areas for both models. One 

area in which the groundwater and surface-water divides are 

not coincident is the Chipuxet River subbasin in the eastern 

Pawcatuck River model (fig. A3–2). In this area, groundwater 

flows to the east across the surface-water divide into the 

Annaquatucket River Basin. To account for this, the eastern 

no-flow boundary in the eastern Pawcatuck River model 

was shifted to the west from the surface-water divide to be 

coincident with the groundwater divide determined from the 

results of groundwater-flow-model simulations of the HuntAnnaquatucket-Pettaquamscutt stream-aquifer system (Barlow 

and Dickerman, 2001).

In areas where the models did not extend to an upland-till 

surface-water divide—namely, across river valleys—specified 

flows were assigned to the model cells closest to the points 

where rivers entered the active modeled areas. These specified 

flows were derived from the hydrograph-separation analysis 

(Rutledge, 1998) described in Part 1. The lower Wood River 

model included five of these cells, and the eastern Pawcatuck 

River model included one (fig. A3–1).

The upper boundary of the model was the water table, 

which was a free-surface boundary that received spatially 

variable recharge from precipitation. The lower boundary of 

the model was the crystalline bedrock that underlies the entire 

study area. The bottom of the model was set at 50 ft below the 

bedrock surface to allow for the simulation of groundwater 

flow in the upper, more weathered, part of the bedrock. 

The lateral boundaries of the model, through which 

all groundwater discharged to streams and the coast, were 

represented in the model as either head-dependent flux 

boundaries or constant-head boundaries. The head-dependent 

flux boundaries were used to simulate the interaction between 

groundwater and surface water in the streams throughout the 

basin. The constant-head boundaries were used in the eastern 

Pawcatuck River model to simulate groundwater discharge to 

the coastal waters along the southern boundary of the model.

The stream boundaries were simulated by the StreamRouting Package (STR) (Prudic, 1989), which allows for the 

hydrologic interaction between the aquifer and the adjoining 

streams and routes water between adjacent stream reaches. 

Discharge fluxes to the streams are calculated by the model 

on the basis of the hydraulic gradient between the modelcalculated head in the model cell representing the stream 

and the specified-boundary head and hydraulic conductance 

at the boundary face. The boundary heads specified for the 

streams simulated by the STR package were set equal to the 

stream-stage altitudes estimated from the 1:24,000 USGS 

topographic-map hypsography for the study area (P.A. 

Steeves, U.S. Geological Survey, written commun., 2004). 

The hydraulic conductance was calculated for each model cell 

representing a stream (McDonald and Harbaugh,1988) as

C K W L

M = ( )( )( )

( ) , (1)

where

C is the hydraulic conductance of the streambed 

(ft2/d),

K is the vertical hydraulic conductivity of 

streambed deposits (ft/d),

W is the width of the stream (ft),

L is the length of the stream within the model 

cell (ft), and

M is the thickness of the streambed (ft).

The parameters used in equation 1 to calculate the 

hydraulic conductance (C) were assumed to be the same for all 

streams and rivers. The simulated vertical hydraulic conductivity of the streambed deposits (K) was set equal to 30 ft/d, a 

value similar to that of the surrounding aquifer. The width (W) 

of the streams was assumed to be 5 ft, the length (L) was set 

equal to the length of the model cell representing the stream 

(100 ft for the lower Wood River model and 250 ft for the 

eastern Pawcatuck River model), and the streambed thickness 

was assumed to be 5 ft. 

The resulting conductance value of 7,500 ft2/d in the 

eastern Pawcatuck River model was adjusted downward 

to 2,500 ft2/d, similar to the value calculated for the lower 

Wood River model, to minimize the mass-balance errors 

from simulations that utilized the higher conductance 

value. Justification for this adjustment can be found in the 

MODFLOW documentation (McDonald and Harbaugh, 1988), 

which states that in the absence of detailed field measurements 

of streambed characteristics, a conductance value must be 

chosen more or less arbitrarily and may need to be adjusted 

during model calibration. Adjustments to these parameters 

may affect the locations and magnitudes of model-calculated 

fluxes to and from these simulated surface-water bodies; localscale analyses of specific surface-water bodies may require the 
200 Appendix Part 3. Development of Groundwater Flow Models

collection of more detailed hydrologic data than was possible 

for this regional analysis.

Constant-head boundaries are used to represent large 

surface-water bodies, such as the coastal-water boundary of 

the eastern Pawcatuck River model. It is assumed that flow to 

or from these water bodies will not affect their water levels. 

The amount of water flowing between the surface-water body 

and the aquifer in the model depends upon the groundwater 

heads in the model cells that surround the specified-head 

boundary (Reilly, 2001). 

The constant-head boundary used for the salt-pond 

coastal-water bodies along the southern Rhode Island coast 

in the eastern Pawcatuck River model was set at a uniform 

value of 2.0 ft above the National Geodetic Vertical Datum 

of 1929 (NGVD 29), this value was similar to the value used 

in the previous model developed for coastal Rhode Island 

(Masterson and others, 2007). The southern part of the eastern 

Pawcatuck River model was extended southward to the Rhode 

Island coastline because of the uncertainty in the position of 

the groundwater divide that separates the Pawcatuck River 

Basin from the South Coastal Basin. Simulations by the model 

developed for coastal Rhode Island (Masterson and others, 

2007) showed that adjusting the constant head up or down 

by 1.0 ft had little effect on model-calculated fluxes to these 

coastal waters.

Temporal Discretization and Initial Conditions

The simulation period for this investigation from January 

2000 through September 2004 was subdivided, or discretized, 

into 75 stress periods. The first stress period simulated the 

average pumping and recharge conditions for the study 

period by using the steady-state option in MODFLOW–2000 

(Harbaugh and others, 2000). The remaining 74 stress periods 

were subdivided into monthly periods of 28 to 31 days with 

the exception of the months May through September 2002, for 

which 22 weekly stress periods were used. The 2002 summer 

period was more finely discretized because it included the 

lowest streamflows observed during the simulation period, and 

the finer time discretization allowed for a more accurate model 

representation of the measured changes in streamflow under 

low-flow conditions. Daily time steps were used for each of 

the monthly stress periods and half-day time steps were used 

for the weekly stress periods to improve model stability and to 

minimize mass-balance errors. 

Hydrologic Stresses

The hydrologic stresses simulated in the model included 

recharge from precipitation and pumping for water supply 

and turf-farm irrigation. These stresses were varied between 

successive weekly and monthly stress periods. The recharge 

estimates were derived from the HSPF model (Part 2), and the 

pumping rates for production and irrigation wells are presented in Part 1.

Recharge

Recharge rates were specified in the two models on the 

basis of the active groundwater component of the HSPF model 

for the Pawcatuck River Basin. Recharge rates were specified 

for three distinct zones defined according to the hydrogeologic 

characteristics assigned to these zones in each model. These 

zones were the glacial stratified deposits, upland till areas, and 

wetlands (shown in figs. A3–1 and A3–2). The areal average 

recharge rate used in the two models for the study period was 

about 22.7 in/yr. In the lower Wood River model, this rate 

was derived from recharge rates of 32.9 in/yr for the stratified 

glacial deposits, 21.5 in/yr for the upland till, and -4.2 in/yr 

for the areas covered by wetlands. In the eastern Pawcatuck 

River model, this rate was derived from recharge rates of 

33.4 in/yr for the stratified glacial deposits, 23.3 in/yr for 

the upland till, and -4.2 in/yr for the areas covered by wetlands. Because upland till areas are characterized by lower 

permeability, greater topographic relief, and the potential for 

more overland runoff than valley-fill deposits, it is generally 

assumed that recharge in upland till is less than in glacial 

stratified deposits, although no field data were available to 

quantify the difference in this study.

The aggregate recharge rate of about 22.7 in/yr is consistent with values that were initially derived from hydrographseparation techniques and adjusted during model calibration 

in previous studies in Rhode Island (Dickerman and others, 

1997; Barlow and Dickerman, 2001; Granato and others, 

2003; Friesz, 2004; Zarriello and Bent, 2004). This rate is 

nonetheless lower than what was reported previously for longterm average conditions for this area because it represents 

the average of the study period only, January 2000 through 

September 2004, rather than the longer time period associated 

with the previous studies. 

Recharge in wetlands is also poorly understood and 

subject to a large degree of uncertainty, but it is believed to 

vary greatly depending on the extent of open water, type of 

vegetation, the location of the wetland within the flow system, 

and whether the wetlands have surface-water outflows. For 

this reason, recharge rates for wetlands simulated in numerical 

models are often determined through model calibration rather 

than by field measurements. 

The development of the models for the Pawcatuck River 

Basin was based on the assumption that nearly all of the ponds 

and wetlands are hydrologically connected to the Pawcatuck 

River and its associated tributaries. Because precipitation 

on ponds and wetlands was assumed to flow out of the basin 

through the stream network, no simulated recharge reached 

the underlying aquifer in these areas. For the period from late 

spring to early fall, it was assumed that the evapotranspiration 

rate exceeded the precipitation rate; this excess resulted in a 

net water change of -4.2 in/yr in wetland areas.

It was assumed for the purpose of this investigation that 

no water was returned to the aquifer from irrigation or from 

onsite domestic septic systems. Irrigation of turf farms is the 

predominant agricultural use of pumped water in the basin, 
Hydraulic Properties 201

and it was assumed that during the growing season, April to 

October, all of the water pumped for irrigation was lost to 

evapotranspiration. The water pumped for municipal supply 

was exported out of the basin (Wild and Nimiroski, 2004) and 

thus removed from the groundwater-flow system. Water use 

from small-capacity domestic-supply wells was not considered in this analysis; it was assumed that, because most of this 

water was returned to the aquifer through nearby onsite septic 

systems, there was no net change in flow in the aquifer.

Pumping

Pumping for municipal supply was simulated in the 

eastern Pawcatuck River model from wells in the town of 

Kingstown from the Kingstown Water Department, United 

Water of Rhode Island, and the University of Rhode Island. 

The average total pumping rate simulated for the study period 

was about 3.4 Mgal/d. A detailed discussion of the simulated 

changes in pumping rate for municipal supply and turf irrigation is included in Part 1.

Hydraulic Properties

The hydraulic properties required as input data for the 

simulation of groundwater flow are the horizontal and vertical 

hydraulic conductivity of the aquifer and aquifer storage. The 

hydraulic conductivity values initially specified in the flow 

model were assigned on the basis of aquifer-test, lithologic, 

and geologic information (Gonthier and others, 1974; Melvin 

and others, 1992) as well as information published in previous 

modeling investigations in southern Rhode Island (Dickerman 

and others, 1990, 1997; Barlow and Dickerman, 2001; Granato 

and others, 2003; Friesz, 2004). Hydraulic conductivity values 

for stratified glacial deposits were assigned on the basis of 

grain-size categories and geologic processes of deposition. A 

detailed discussion of the geologic setting of the Pawcatuck 

River Basin can be found in Part 1. The relation between 

geologic framework and hydraulic conductivity values from a 

similar model of groundwater flow in southern Rhode Island 

(Masterson and others, 2007) was used in this investigation.

The range in hydraulic conductivity values specified in 

the flow models is listed in table A3–1 for the deposits shown 

on figures A3–1 and A3–2. An example of the distribution of 

hydraulic conductivity values used in the calibrated model is 

shown for cross-section X–X′ (fig. A3–3). 

Surface-water bodies, such as ponds and wetlands, were 

simulated as part of the aquifer system and assigned hydraulic 

properties. It was assumed that the ponds were in direct 

hydraulic connection to the aquifer and that they provided 

no effective resistance to flow. As a result, groundwaterflow lines converged toward ponds in upgradient areas 

where groundwater discharges to ponds, and diverged in 

downgradient areas where ponds recharge the aquifer. Ponds 

in the model were simulated as areas of high hydraulic 

conductivity (50,000 ft/d), more than two orders of magnitude 

higher than the values for hydraulic conductivity specified in 

surrounding aquifer (table A3–1).

It was assumed that the surfaces of wetlands had a greater 

resistance to horizontal flow than the kettle-hole ponds, but 

less resistance to flow than the surrounding aquifer. As a 

result, wetland areas were assigned a horizontal hydraulic conductivity value of 5,000 ft/d and a vertical hydraulic conductivity value of 5 ft/d (anisotropy of 1,000:1). 

The peat deposits that underlie the wetlands were 

assigned a hydraulic conductivity value of 1.0 ft/d to account 

for the highly decomposed peat and organic-rich silts beneath 

the wetlands (Friesz, 2004). It was assumed that the peat 

deposits are highly anisotropic; the vertical hydraulic conductivity of these deposits was specified as 0.01 ft/d (anisotropy 

of 100:1) (table A3–1).

The streambed deposits were assumed to be much 

more permeable than the wetland peats and more similar to 

the surrounding aquifer. As a result, the vertical hydraulic 

conductivity value used to determine the conductance 

discussed previously in the section “Hydrologic Boundaries” 

was 30 ft/d, the vertical hydraulic conductivity associated 

with a horizontal hydraulic conductivity of 150 ft/d and an 

anisotropy of 5:1 for sand and gravel deposits (table A3–1). 

Table A3–1. Hydraulic conductivity values of the lithologic units 

simulated in the groundwater-flow models in the Pawcatuck 

River Basin, southwestern Rhode Island.

Lithologic deposit

Horizontal 

hydraulic 

conductivity 

(feet per day)

Anisotropy

Stratified glacial deposits

Sand and gravel 150–350 5:1 to 3:1

Fine/medium sand 70–125 30:1 to 10:1

Fine sand and silt 10–30 100:1 to 10:1

Silt and clay 0.01–10 1:1 to 100:1

Moraines 10–70 100:1 to 30:1

Peat 1.0 100:1

Till 1–5 10:1

Bedrock 1.0 10:1
202 Appendix Part 3. Development of Groundwater Flow Models

The remaining hydraulic property represented in the 

models is the storage term, which is required to quantify the 

volume of water that an aquifer releases from or takes into 

storage per unit surface area of the aquifer per unit change 

in head (Heath, 1989). The storage capacity of the aquifer 

controls, in part, the degree to which water levels fluctuate 

in the aquifer in response to seasonal changes in recharge, 

changes in pumping rates, and the timing of the release of 

groundwater to streams. 

Storage properties were assigned in the models on the 

basis of the same hydrogeologic units used to assign the 

hydraulic conductivity values. Storage was specified in the 

model as a dimensionless storage coefficient as a feature of the 

fixed-transmissivity approach, which is based on the assumption of confined conditions in all of the model layers. The 

storage coefficient terms specified for layer 1 were assumed 

to represent specific yield and were 0.23 for glacial stratified 

deposits, 1.0 × 10-7 for upland till, and 1.0 for the surfacewater bodies.

The upland till areas were assigned low storage values—

much lower than published values to compensate for the 

inability of the model to simulate properly the seasonally 

varying dewatering of these upland areas in layer 1. This 

limitation is a consequence of the fixed-transmissivity 

approach, which would otherwise result in unrealistically large 

water releases of water from storage during the dry summer 

months when presumably the upland till areas would dry out 

and no longer transmit water to the glacial stratified deposits 

(DeSimone, 2004).

Surface-water bodies, including ponds, streams, and wetlands, were all assigned a storage value of 1.0 to represent the 

maximum porosity and storage capacity for the water column 

which was explicitly represented as aquifer material in the 

flow models. These high values used in layer 1 resulted in the 

dampened fluctuations in water levels in response to seasonal 

changes in recharge. 

In the lower model layers, the storage coefficient for the 

confined glacial stratified deposits and bedrock was set to 

1.0 × 10-5 and the storage coefficient for upland till areas 

remained 1.0 × 10-7. The aquifer sediments beneath the 

surface-water bodies consist of glacial stratified deposits 

and were represented as such with respect to simulated 

storage properties.

Model Calibration and Limitations

Model calibration is the process by which initial modelinput parameters are modified to make simulated results more 

closely match observed water levels and streamflows (Reilly 

and Harbaugh, 2004). The adequacy of the calibration is based 

to a large degree on the intended use of the results and thus 

can differ among investigations. For this investigation, the primary use of the groundwater-flow models for the lower Wood 

River and eastern Pawcatuck River subbasins was to provide 

an analysis of the response of the groundwater-flow system to 

changes in groundwater withdrawals. This analysis included 

a comparison of the changes in model-calculated water levels 

and streamflows for different pumping scenarios. 

As a result, the calibration of these particular models 

focused on matching the magnitudes of measured change 

in water levels and streamflows during the study period 

rather than matching the absolute values of measured water 

levels and streamflows. Water-level data from previous 

investigations, however, were used to show that the 

water levels simulated for steady-state conditions in this 

investigation provided a reasonable match to previously 

measured water levels (tables A3–2 and A3–3) given that 

the recharge conditions at the time those measurements were 

made differ from those observed during the study period. Data 

from previous investigations included the water-level data 

published for the lower Wood River model for October 1976 

(Dickerman and others, 1990) and for the Usquepaug-Queen 

area of the eastern Pawcatuck River model for September 

1989 (Dickerman and others, 1997). 

A comparison of the model-calculated water levels to 

those that were measured throughout the study period provides 
Model Calibration and Limitations 203

a better measure of how well the models in this investigation 

simulated the changes in water levels with time. The water 

levels used in this comparison were measured in one observation well in the lower Wood River model area (RIW–785) 

(fig. A3–1) and in three observation wells in the eastern 

Pawcatuck River model area (EXW–554, RIW–417, and 

SNW–006) (fig. A3–2). The comparisons between the measured and model-calculated water levels for these wells are 

shown in figures A3–4A–D. In general, the changes in modelcalculated water levels throughout the study period agreed 

well with the measured water levels. 

The differences in the absolute values between measured 

and modeled water levels in these observation wells can be 

partially attributed to the effects of the representation of the 

stream network in the modeled area. In narrow valley-fill sand 

and gravel aquifers, such as those in the northeastern part of 

the Pawcatuck River Basin, the simulated streambed altitudes 

assigned to the model cells can greatly affect the water levels 

in the surrounding aquifer. Discrepancies between streambed altitudes specified in the model according to the digitalelevation data and the actual streambed altitudes can result in 

several feet of deviation of the model-calculated water levels 

from those measured in the field. Also, the effect of grid discretization on the geometry of the simulated stream network 

may result in an overrepresentation of the effect of the stream 

on the simulated water levels in the surrounding aquifer. This 

effect is more apparent when the model cells representing 

streams are much wider than the actual stream channel.

The calibration of the groundwater-flow model with 

respect to streamflow was based on a comparison of modelcalculated streamflows to those determined by the hydrographseparation techniques described in Part 1. A comparison of 

model-calculated to measured streamflows is presented in 

figures A3–5A–I for the outlet points of the HSPF subbasins 

described in Part 2.

Given the limitations of the calibration data coupled with 

the objectives of the model-calibration process, only minor 

adjustments were made to the initially specified hydraulic 

conductivity values. The storage coefficient term used to represent the upland till areas was adjusted downward to a value 

much lower than values previously reported for similar hydrogeologic settings so that the responses of the model-calculated 

water levels and streamflows to seasonal changes in recharge 

better matched the observed transient data. The recharge rates 

simulated in the models were determined by the HSPF model 

and were not modified during the calibration process in order 

to maintain a consistent water balance between the HSPF and 

MODFLOW models. 

Adjustments also were made to the hydraulic properties 

to resolve large-scale, regional inconsistencies between the 

field data and the simulation results rather than to match individual calibration targets of observed water levels and streamflows. The fixed-transmissivity approach used to develop the 

flow models limits the maximum pumping rates that can be 

simulated in the flow models. If the simulated pumping rate of 

a given well site would result in a drawdown of the water table 

that is greater than 10 percent of the saturated thickness in that 

area then the fixed-transmissivity approach may result in an 

overrepresentation of the aquifer transmissivity, and therefore, an underrepresentation of the actual drawdown from that 

pumping rate (Reilly and Harbaugh, 2004). 

The flow models developed for this investigation at best 

represent idealized conceptualizations of actual hydrogeologic 

conditions. The accuracy of the model predictions presented in 

this analysis are a function of the quality of the input calibration data, and how realistic were the assumptions of future 

pumping and recharge rates. Although, individual pumping 

rates and well locations will invariably change as water-management plans evolve over time; however, the use of numerical models developed according to a well-reasoned conceptual 

model of the aquifer system, with an understanding of the 

limitations of the simulation results, can provide valuable tools 

for improving the understanding of groundwater and surfacewater interactions in the Pawcatuck River Basin.
204 Appendix Part 3. Development of Groundwater Flow Models

Table A3–2. Model-calculated and measured groundwater levels in the lower Wood River model area in 

the Pawcatuck River Basin, southwestern Rhode Island.—Continued

[ID, identifier; Residual, residual equals measured minus model-calculated water levels. Measured water-level data derived 

from Dickerman and others (1990). Water-level values are in feet relative to NGVD 29]

Well ID Stateplane-X 

coordinate

Stateplane-Y 

coordinate

Model 

layer

 Water levels

Measured Model-calcluated Residual

CHW–226 274897.94 127118.23 1 42.1 41.9 0.2

CHW–426 277568.58 129237.94 1 43.0 42.3 0.7

CHW–429 277947.3 128224.99 1 46.0 43.8 2.2

RIW–231 273926.49 135420.07 1 59.2 59.6 -0.4

CHW–226 274897.94 127118.23 1 42.1 41.9 0.2

CHW–265 278549.97 124984.86 1 50.7 46.2 4.5

CHW–299 280089.27 132775.27 1 53.2 45.4 7.8

CHW–305 281082.1 134190.31 1 51.1 45.7 5.3

CHW–428 277489.63 127922.31 1 42.0 42.8 -0.8

HOW–291 268447.57 136951.38 1 54.1 52.6 1.5

HOW–300 264053.79 145363.72 1 80.4 75.8 4.6

HOW–425 269153.64 145350.54 1 57.0 55.0 2.0

RIW–253 275283.3 129141.67 1 47.1 48.0 -0.9

RIW–254 270201.09 137858 1 47.7 53.9 -6.2

RIW–257 271418.63 137551.42 1 57.2 56.1 1.1

RIW–284 274902.68 129243.74 1 48.2 48.9 -0.7

RIW–288 274907.18 131268.03 1 52.7 52.4 0.3

RIW–289 273759.22 128841.45 1 47.4 48.5 -1.1

RIW–291 272463.63 128540.79 1 52.0 47.7 4.3

RIW–294 269500.16 131483.13 1 49.0 48.8 0.2

RIW–418 270371.26 145246.35 1 60.0 57.8 2.2

RIW–419 269607.85 144337.26 1 58.0 55.3 2.7

RIW–420 270976.32 143625.43 1 66.0 59.0 7.0

RIW–421 271282.26 144231.99 1 66.0 59.7 6.3

RIW–422 272041.8 143521.68 1 66.0 60.9 5.1

RIW–428 271735.87 142915.11 1 65.7 60.3 5.4

RIW–430 271807.7 141093.05 1 64.3 59.6 4.7

RIW–432 270968.56 140386.54 1 63.3 58.3 5.0

RIW–438 271727.74 139473.79 1 62.6 58.8 3.8

RIW–440 271800.77 138157.81 1 60.9 57.5 3.4

RIW–443 271113.33 137248.51 1 56.6 55.3 1.3

RIW–444 271113.33 137248.51 1 56.6 55.3 1.3

RIW–447 271265.14 137045.71 1 56.5 55.2 1.3

RIW–448 270959.84 136742.79 1 56.3 53.8 2.5

RIW–449 270959.84 136742.79 1 56.1 53.8 2.3
Model Calibration and Limitations 205

Table A3–2. Model-calculated and measured groundwater levels in the lower Wood River model area in 

the Pawcatuck River Basin, southwestern Rhode Island.—Continued

[ID, identifier; Residual, residual equals measured minus model-calculated water levels. Measured water-level data derived 

from Dickerman and others (1990). Water-level values are in feet relative to NGVD 29]

Well ID Stateplane-X 

coordinate

Stateplane-Y 

coordinate

Model 

layer

 Water levels

Measured Model-calcluated Residual

RIW–450 271265.14 137045.71 1 56.5 55.2 1.3

RIW–452 270351.17 136946.69 1 55.8 52.3 3.5

RIW–453 272559.11 136840.23 1 55.7 57.9 -2.2

RIW–454 270579.6 136946.14 1 55.9 53.1 2.8

RIW–456 274385.44 136329.97 1 64.0 61.2 2.8

RIW–457 274688.43 135620.78 1 62.0 60.6 1.4

RIW–462 272785.9 136131.19 1 58.6 58.1 0.5

RIW–463 272785.9 136131.19 1 58.6 58.1 0.5

RIW–465 273241.15 135421.63 1 58.5 58.7 -0.2

RIW–467 271567.55 136134.05 1 57.5 55.3 2.2

RIW–468 271262.97 136134.78 1 56.5 54.2 2.3

RIW–470 272325.71 134715.25 1 58.2 57.3 0.9

RIW–471 272325.71 134715.25 1 58.1 57.3 0.8

RIW–472 273620.28 134712.26 1 58.2 58.9 -0.7

RIW–475 271638.91 134109.57 1 61.0 55.7 5.3

RIW–476 275216.54 133392.86 1 56.0 56.9 -0.9

RIW–477 272931.64 133296.82 1 65.0 56.1 8.9

RIW–479 273462.42 132283.45 1 63.0 57.1 5.9

RIW–485 276129.08 132783.57 1 52.3 54.0 -1.7

RIW–486 276129.08 132783.57 1 52.8 54.0 -1.2

RIW–488 276128.42 132479.92 1 52.4 52.9 -0.5

RIW–489 276128.42 132479.92 1 54.0 52.9 1.1

RIW–490 275974.78 131872.97 1 51.3 51.2 0.1

RIW–491 275974.78 131872.97 1 51.6 51.2 0.4

RIW–492 276505.28 130657.23 1 47.2 47.9 -0.7

RIW–493 276505.28 130657.23 1 48.8 47.9 0.8

RIW–495 277955.59 132172.37 1 53.0 44.8 8.2

RIW–496 271786.68 132186.13 1 59.0 53.0 6.0

RIW–497 272243.64 132185.05 1 64.0 54.8 9.2

RIW–498 274908.99 132077.75 1 57.0 54.4 2.6

RIW–524 271631.49 130971.91 1 57.0 51.6 5.4

RIW–525 269040.19 130269.68 1 49.0 47.9 1.1

RIW–526 274220.13 130561.06 1 56.0 52.1 3.9

RIW–528 273685.13 129752.56 1 51.0 52.8 -1.8

RIW–631 275057.04 130154.33 1 46.3 50.0 -3.7
206 Appendix Part 3. Development of Groundwater Flow Models

Table A3–3. Model-calculated and measured groundwater levels in the Eastern Pawcatuck River model 

area in the Pawcatuck River Basin, southwestern Rhode Island.

[ID, identifier; Residual, residual equals measured minus model-calculated water levels. Measured water-level data derived from 

Dickerman and others (1997). Water-level values are in feet relative to NGVD 29]

Well ID Stateplane-X 

coordinate

Stateplane-Y 

coordinate Model layer

Water levels

Measured Model-calcluated Residual

EXW–553 311039 175548 1 145.3 149.3 -4.0

EXW–554 316357 169269 1 144.9 143.2 1.7

EXW–555 313315 168562 1 132.9 132.9 0.0

EXW–556 309891 165528 1 125.2 122.7 2.5

EXW–558 309131 166035 1 120.6 120.5 0.1

EXW–559 308294 166440 1 122.4 123.8 -1.4

EXW–560 308136 159254 1 122.6 122.3 0.3

EXW–561 311795 169474 1 129.1 128.2 0.9

RIW–188 296634 147323 1 99.5 99.4 0.1

RIW–780 296629 144185 1 100.3 98.0 2.3

RIW–782 298531 143373 1 98.4 96.2 2.2

SNW–311 300680 158350 1 113.2 114.2 -1.0

SNW–314 302198 155009 1 117.1 114.3 2.8

SNW–515 299603 148129 1 101.4 99.5 1.9

SNW–1192 305850 154600 1 119.4 117.0 2.4

SNW–1193 304632 153994 1 118.6 115.7 2.9

SNW–1194 302276 156729 1 117.4 114.7 2.7

SNW–1195 302804 152376 1 111.9 111.3 0.6

SNW–1196 301587 153187 1 113.1 111.6 1.5

SNW–1197 298924 152988 1 108.2 107.1 1.1

SNW–1198 301050 149342 1 104.8 102.8 2.0

SNW–1199 300206 143573 1 95.6 94.1 1.5

SNW–1200 298995 148939 1 100.8 99.4 1.4
Model Calibration and Limitations 207

Figure A3–4A. Comparison of measured and model-calculated groundwater levels for well RIW–417 in the 

eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site location 

shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and November for 

years shown. Steady state (SS) represents average steady-state conditions for simulation period.

107

108

109

110

111

112

RIW-417

2000 2001

Measured

Model calculated

2002 2003 2004

J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

WATER-TABLE ALTITUDE, IN FEET ABOVE NGVD 29

SS

A
208 Appendix Part 3. Development of Groundwater Flow Models

Figure A3–4B. Comparison of measured and model-calculated water levels for well SNW–006 in the eastern 

Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site location shown 

in figure A3–2. Months shown on x-axis are January, March, May, July, September, and November for years 

shown. Steady state (SS) represents average steady-state conditions for simulation period.

96

98

100

102

104

106

108

SNW-006

Measured

WATER-TABLE ALTITUDE, IN FEET ABOVE NGVD 29

Model calculated

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

B
Model Calibration and Limitations 209

Figure A3–4C. Comparison of measured and model-calculated water levels for well EXW–554 in the lower Wood 

River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site location shown in figure A3–2. 

Months shown on x-axis are January, March, May, July, September, and November for years shown. Steady 

state (SS) represents average steady-state conditions for simulation period.

140

145

150

EXW-554

Measured

WATER-TABLE ALTITUDE, IN FEET ABOVE NGVD 29

Model calculated

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

C
210 Appendix Part 3. Development of Groundwater Flow Models

Figure A3–4D. Comparison of measured and model-calculated water levels for well RIW–785 in the lower 

Wood River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site location shown in figure 

A3–1. Months shown on x-axis are January, March, May, July, September, and November for years shown. 

Steady state (SS) represents average steady-state conditions for simulation period.

56

57

58

59

60

61

62

63

64

RIW-785

Measured

WATER-TABLE ALTITUDE, IN FEET ABOVE NGVD 29

Model calculated

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

D
Model Calibration and Limitations 211

0

10

20

30

40

50

60

70

80

90

100

110

120

130

QUEN4 (RCHRES 9, 01117370)

BASEFOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

A

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5A. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet QUEN4 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
212 Appendix Part 3. Development of Groundwater Flow Models

50

0

100

150

200

QUEN6 (RCHRES 19, 01117410)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

B

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5B. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet QUEN6 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
Model Calibration and Limitations 213

50

0

100

150

200

250

QUEN7 (RCHRES 20, 01117420)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

C

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5C. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet QUEN7 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
214 Appendix Part 3. Development of Groundwater Flow Models

5

10

15

20

25

30

35

40

0

CHIP1 (RCHRES 31, 01117336)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

D

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5D. Comparison of measured and model-calculated baseflows for RCHRES outlet CHIP1 in the 

eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site location 

shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and November for 

years shown. Steady state (SS) represents average steady-state conditions for simulation period.
Model Calibration and Limitations 215

0

10

20

30

40

50

60

CHIP2 (RCHRES 32, 01117350)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

E

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5E. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet CHIP2 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
216 Appendix Part 3. Development of Groundwater Flow Models

0

5

10

15

20

25

30

35

CHIC2 (RCHES 36, 01117424)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

F

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5F. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet CHIC2 in the 

eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site location 

shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and November for 

years shown. Steady state (SS) represents average steady-state conditions for simulation period.
Model Calibration and Limitations 217

50

0

100

150

200

250

300

350

400

450

500

550

600

PAWC3 (RCHRES 46, 01117500)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

G

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5G. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet PAWC3 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
218 Appendix Part 3. Development of Groundwater Flow Models

0

10

20

30

40

50

60

70

BEAV3 (RCHRES 43, 01117471)

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

H

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5H. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet BEAV3 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
Model Calibration and Limitations 219

1

0

2

3

4

5

6

7

8

9

10

11

BASEFLOW, IN CUBIC FEET PER SECOND

Measured

Model calculated

I TANE1 (RCHRES 45, 01117480)

2000 2001 2002 2003 2004

SS J M M J S N J M M J S N J M M J S N J M M J S N J M M J S 

Figure A3–5I. Comparison of measured and model-calculated baseflows for HSPF subbasin outlet TANE1 

in the eastern Pawcatuck River model area in the Pawcatuck River Basin, southwestern Rhode Island. Site 

location shown in figure A3–2. Months shown on x-axis are January, March, May, July, September, and 

November for years shown. Steady state (SS) represents average steady-state conditions for simulation period.
220 Appendix Part 3. Development of Groundwater Flow Models

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