GROUND WATER/SURFACE WATER INTERACTIONS AWRA SUMMER SPECIALTY CONFERENCE Judith Schenk'

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July 1-3 GROUND WATER/SURFACE WATER INTERACTIONS AWRA SUMMER SPECIALTY CONFERENCE 2002 326x6 pjf= INTEGRATION OF DATA USING GIS AND STATEPP TO ESTIMATE GROUNDWATER MODEL INPUT PARAMETERS Judith

1 July 1-3 GROUND WATER/SURFACE WATER INTERACTIONS AWRA SUMMER SPECIALTY CONFERENCE x6 pjf= INTEGRATION OF DATA USING GIS AND STATEPP TO ESTIMATE GROUNDWATER MODEL INPUT PARAMETERS Judith Schenk' ABSTRACT The State of Colorado is developing the Colorado Decision Support System as a management system for surface water and groundwater resources. The Rio Grande Decision Support System (RGDSS) includes a ground-water model of the San Luis Valley in southem Colorado as one of the modeling components. Data sources used to create the ground-water model input files include results from a consumptive-use model and a surface-water model. GIS data of land use, vegetation distribution, and rim inflow areas, surface water flow and diversion data, rim inflow recharge estimates, and precipitation data are used to estimate model parameters. A preprocessing program, STATEPP, has been developed to integrate these data and create ground-water model input files. The data centered approach used in RGDSS results in continuity of data among the models (consumptive use, surface water, and ground water) and allows for easy generation of new input files when data are updated. KEY TERMS: ground-water model; surface water; consumptive use; RGDSS; STATEPP; San Luis Valley. INTRODUCTION The State of Colorado is developing the Colorado Decision Support System (CDSS) as a management tool for decision regarding surface water and ground water resources for major water basins within the state boundary. The Rio Grande Decision Support System (RGDSS) includes modeling components for crop consumptive use, surface water, and ground water. This paper discusses how data from the surface-water model, consumptive-use model, and spatial data are integrated using a preprocessing program, STATEPP (Schenk and Palumbo, 2002), to produce drain, evapotranspiration, recharge, and well input files for the ground water model. STATEPP is designed to allow for ease of updating ground-water model files when additional data become available. The ground-water model for RGDSS includes ground-water resources in the San Luis Valley in south central Colorado. The ground-water model was developed using the U.S. Geological Survey three-dimensional groundwater flow model, MODFLOW (McDonald and Harhaugh, 1988). Data for the model came from the following sources: 1) spatial data, 2) surface-water data, 3) consumptive-use data, and 4) ground-water records (pumping, water levels in wells). The challenge is to have agreement between results of the surface-water model, consumptiveuse model, spatial data, and the ground-water model. This paper discusses how these data are integrated using STATEPP to create drain, evapotranspiration, recharge, and well files used in the ground-water model. In addition to RGDSS, STATEPP can he used for other CDSS projects. STUDY AREA The San Luis Valley encompasses approximately 3100 square miles and is bordered by the Sangre de Cristo mountains to the east and north, and the San Juan mountains to the west and north (Figure 1). The climate is semiarid with average precipitation of six to ten inches annually. Snowfall accounts for less than one third of precipitation on the valley floor. The source of ground water in the valley is primarily from snowmelt in the mountains, leakage through canals, excess water from irrigation, and precipitation. Agricultural drains and flowing wells (artesian wells that are allowed to flow without restriction) are present in the valley. The San Luis Valley is divided into two drainage basins. Streams to the north of the Rio Grande, such as San Luis Creek and Saguache Creek, flow towards the Closed Basin area located to the west of Great Sand Dunes National Park. Groundwater in the northern portion of the valley flows towards this area and the only means of discharge is by evapotranspiration or pumping. The groundwater divide exists just north of the Rio Grande where the Rio Grande NUS a south-east course. Streams south of the Rio Grande, such as Trinchera Creek, Culebra Creek, Alamosa River, La Jara Creek, San Antonio River, and the Conejos River, are tributaries to the Rio Grande. ' Hydrogeologist, HRS Water Consultants Inc., 8885 West 14' Avenue, Lakewood, CO 80215, Phone: (303) , Fax (303) , jschenk@hrswater.com 323

2 The ground water model contains 5 layers, 196 rows, and 116 columns. General head boundaries are used for the west boundary in layers 2,3, and 4. Constant head boundaries are used in layers 1 to 4 for the south boundary. There are several thousand agricultural wells in the valley. Two hundred and forty eight surface-water diversions are located along streams simulated in the model Mik Figure 1. San Luis Valley study area. CREATION OF MODFLOW DRAIN FILE The drain file includes information about agricultural drains, springs, and flowing wells. Flowing wells in the San Luis Valley are low capacity wells (commonly less than 50 gpm) completed in the upper portion of the confined aquifer. These wells are left to flow without limit throughout the year. Flowing wells are modeled as drains that discharge from the upper portion of the confmed aquifer (layers 2 and 3 in the model). A percentage of the flow from the flowing wells is estimated to recharge the top layer of the model. The drain package in MODFLOW has been modified to allow for this recharge. The exact locations of flowing wells are not known. Their location is estimated using the location of known low-capacity wells (less than 50 gpm) in the valley. These data are provided in the form of layer, row, and column location in the MODFLOW ground water grid. Spatial data for the location of agricultural wells are used to create an initial drain fde. This is done with a MODFLOW user interface, GMS. This initial drain file, spatial data on the location of low capacity wells, and additional user information are used as input into STATEPP to produce a fmal drain file (Figure 2). The user input includes information about conductance parameters and the percent of flowing well discharge to be retumed as recharge to layer

3 Location of 4 0 gpm wells in ground-water model grid Agricultural Drains Springs + User Input Data MODFLOW Interface Parameters for flowing well conductance GMS Percent of flowing well discharged returned +. as recharge to top layer Initial Drain File A 1 S T j E P P Final MODFLOW Drain File Figure 2. Creation ofthe MODFLOW drain tile. CREATION OF MODFLOW EVAPOTRANSPIRATION FILE Evapotranspiration (ET) functions are developed for the model based on a GIS coverage of vegetation types in the study area and published data on evapotranspiration in the San Luis Valley and other areas with similar conditions. These ET functions are piecewise linear functions which are representative of non-linear ET functions for the different vegetation categories. The ET package was modified to allow for piecewise linear functions for ET. Spatial data on vegetation types are provided to STATEPP in the form of vegetation type, model grid location, and area occupied in each grid cell containing that vegetation type. The user enters information on vegetation categories, vegetation types included in each category, an ET function for each category, and land surface elevation for each active grid cell in the ground-water model (Figure 3). Vegetation types are defmed from satellite imagery of the study area. Vegetation types are combined into broader categories and a piecewise linear ET function is defmed for each category. For example, phreatophytes, hydrophytes, and wetlands are combined under one category, and one piecewise linear ET function is developed for this category. A grid cell typically has multiple vegetation categories. The proportion of the area occupied by each vegetation category to the total area of the grid cell is calculated. The evapotranspiration functions for each vegetation category are weighted by the proportion of the area occupied by the vegetation category to develop one equivalent ET function for a grid cell. Distribution of native Vegetation types in ground-water model grid r n d \ d STATEPP User Input Data Vegetation categories Vegetation types in each category ET function for each vegetation category elevation MODFLOW Evapotranspiration File Figure 3. Creation of MODFLOW evapotranspiration file. 325

CREATION OF MODFLOW RECHARGE FILE Recharge in the Valley represented in the MODFLOW recharge file is from precipitation, rim inflow, canal and ditch leakage, and excess surface water and groundwater

4 CREATION OF MODFLOW RECHARGE FILE Recharge in the Valley represented in the MODFLOW recharge file is from precipitation, rim inflow, canal and ditch leakage, and excess surface water and groundwater from irrigation (Figure 4). The amount of recharge is determined from flow data. The Surface Water Modeling contractor estimates rim inflow recharge. Rim inflows are streams that develop in the mountainous areas around the valley. Many of these streams flow from the mountains in the spring during snowmelt. Seepage from these streams during these rim inflows results in recharge to the aquifers. Recharge from precipitation for a particular county, hydrologic unit code (HUC), for irrigated and non-irrigated land are provided. Flow data for canal leakage and excess surface water and ground water from irrigation comes from the consumptive use model, which, in turn, uses data from the surface water model. Flow data are averaged for each stress period simulated in the ground-water model. Spatial data provides information on where the recharge is to be distributed. Spatial data are represented in the form of location of a feature within the ground-water model grid. Rim inflow zone information is provided in the form of the rim inflow zone name, the grid cells that include the rim inflow zone and the area of a particular grid cell occupied by that rim inflow zone. Spatial data are provided for the countylhuclvegetation type used in the calculation of precipitation recharge. The user inputs which vetgetation types are irrigated. Canals are identified by the structure name (a structure being a canal), and the location and length of each canal reach in a groundwater model grid cell. Irrigated lands are associated with a particular canal and are identified by that structure name. A list of grid cells and the area of the grid cell occupied by the irrigated land associated with a structure are provided in the spatial data. Flow data are averaged for each flow component for each stress period to be simulated in the model. For each canal, the amount of canal leakage is distributed along canal reaches. Rim inflow recharge for each recharge zone is distributed among grid cells that include that rim inflow zone. Recharge for excess surface water and ground water for each structure is distributed among the grid cells with irrigated lands associated with that structure. Each component of recharge is calculated and the total recharge on each grid cell is summed to create the MODFLOW recharge file. Rim Inflow Recharge Rim Inflow zones CountylHUClvegetation type Canals Irrigated Lands Precipitation Recharge Irrigated Lands Non-irrigated Lands STATEPP.c MODFLOW Recharge File * Surface water data Consumptive-use Model Consumptive-use Model Results Leakage from canals Excess surface water Excess ground water Figure 4. Creation of MODFLOW recharge file CREATION OF MODFLOW WELL FILE Well discharge in the San Luis Valley comes from agricultural wells, municipal and industrial wells, and the Closed Basin Project pumping in the closed basin area of the San Luis Valley. In addition, there is some recharge from municipal and industrial well return flows. Estimates of municipal and industrial pumping and return flows, and records of Closed Basin Project pumping are provided to the pre-processor. These data are averaged for each stress period to be simulated in the model and added to the well file (Figure 5). Agricultural pumping is calculated using data from the consumptive use model and spatial data of the location of agricultural wells. The ground-water diversion data (pumping) is given by structure in the consumptive-use 326

5 model results. This pumping data from the consumptive use model is averaged to calculate the amount to be pumped for a structure for each stress period. The pumping is distributed among the wells associated with a structure. This distribution of pumping is done according to permitted well yield and the year the well came on line. Location of irrigation wells in ground-water model grid Municipal and Industrial pumping Closed Basin pumping Consumptive-use Model Results Ground-water diversions MODFLOW Recharge File Figure 5. Creation of MODFLOW well file. SUMMARY The Rio Grande Decision Support system is a data-centered system designed to allow for updating of data and model results associated with RGDSS. The STATEPP program has been developed to process spatial and flow data to create MODFLOW input files for drains, evapotranspiration, recharge, and wells. Spatial data are derived from GIS data. Spatial data includes location of wells with less than 50 gpm permitted yield, native vegetation, canals, irrigated lands, rim inflow zones, county/huc/vegetation combinations, and agricultural wells. Surface water data are used in the consumptive use model. The results of the consumptive use model in turn provide flow data for some components of recharge and for agricultural pumping. Data from the consumptive use model includes leakage estimates from canals, excess surface water and ground water from irrigation, and irrigation pumping. The surface-water modeling contractor provides estimates on rim inflow recharge. Flow data are averaged for each stress period simulated in the ground-water model. STATEPP produces a MODFLOW drain file, evapotranspiration file, recharge file, and well file. Consistency between models used in RGDSS is maintained using this approach. REFERENCES McDonald, M.G. and Harbaugh, A.W., A modular three-dimensional fmite difference ground-water flow model: US. Geological Survey Techniques of Water Resources Investigations, Book 6, Chapter AI, 586 p. Schenk, J. and Palumbo, M., RGDSS Ground Water Task 8 - State Preprocessor, Memorandum to the State of Colorado 327

GROUND WATER/STJRFACE WATER INTERACTIONS JULY 1-5 AWRA SUMMER SPECIALTY CONFERENCE

1997) GROUND WATER/STJRFACE WATER INTERACTIONS JULY 1-5 AWRA SUMMER SPECIALTY CONFERENCE 2002 Surface Water - Groundwater Interaction Represented in the Rio Grande Water Resources Planning Model I 2 Edward