Pitkin County UMRF GW GIS

Development of GIS-Based Ground Water Resources Evaluation

of the Upper and Middle Roaring Fork Valley Area,

Pitkin County, Colorado

Purpose of study

Under an agreement with Pitkin County, Colorado, Hydrologic Systems Analysis, LLC (HSA) of Golden, Colorado and Heath Hydrology, Inc. (HHI) of Boulder, Colorado, created a GIS-based step-wise ground water resources evaluation procedure for use as decision/land use management tools by Pitkin County.  The procedure guides the site-specific analysis with respect to:  1) ground water resources availability in terms of sufficient quantities for the purpose of its usage, and its economical exploitability;  2) long term sustainability of the utilization of the resources for water supply; and  3) the vulnerability of the resources to contamination. The procedure was applied to the valley of the Upper and Middle Roaring Fork River in Pitkin County, resulting in two GIS maps and supporting data bases.

Background

Computer-based GIS maps provide a flexible and efficient way to display and analyze geographic information.  Data from various sources can be collected in local or remotely accessible databases, which can be easily maintained and updated, independently of the display and analysis procedures.  Computer-based GIS maps support optimal usage of data obtained from different sources containing features of significant importance in hydrogeologic evaluations, at different scales, and geographic distribution densities, and with different levels of accuracy and information value.

Details

The GIS layers of the URF and MRF maps contain four types of geographic information: 1) general geographic information (county border, roads, parks, parcels, structures, etc);  2) hydrologic information (precipitation, streams, lakes/ponds, ditches, irrigated areas); 3) hydrogeologic information (alluvial aquifer, hydrogeologic units, wells); and 4) topographic information (topo maps, DEM, 10ft elevation contours).  Type 1 information is used to locate the site of interest and obtain some general geographic data. Type 2 and Type 3 information is integral to the evaluation of ground water resources. Type 4 information provides elevation and background data as needed.  All layers have been georeferenced with respect to Pitkin County's projection and datum: State Plane, Colorado Central Zone, NAD83 (ft).

The GIS maps and data bases, developed for this project, are limited to the area subject to previous studies conducted for Pitkin County by HSA.  The data bases developed for this project include original GIS layers from these studies, as well as GIS layers and data bases from Pitkin County, Colorado Division of Water Resources/Colorado Water Conservation Board, Natural Resources Conservation Survey (USDA), and U.S. Geological Survey.

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Three case history examples are presented to illustrate the analysis procedure, using the GIS maps and data bases provided in this report.  The examples are:  1) Site without available ground water for water supplies in the Middle Roaring Fork area; 2) Site with available ground water for water supplies in the Middle Roaring Fork area; and 3) Site with available ground water for water supplies in the Upper Roaring Fork area.  The two Middle Roaring Fork sites illustrate the variability of drinking water supplies, both in availability and sustainability, within the same region and located near to each other.  The Upper Roaring Fork site illustrates that drinking water supplies are readily available and sustainable for domestic wells in this region.  All three sites are vulnerable to ground water pollution. The examples demonstrate the utility of the presented GIS-based analysis procedure and its advantages over simple, one-layer paper maps showing some general ground water characteristics, and demonstrate the need for site-specific hydrogeologic investigation to obtain quantitative resource management answers and well design parameters.   

Reference

Kolm, K.E., and P.K.M. van der Heijde. November 2005. Development of GIS-Based Ground Water Resources Evaluation of the Upper and Middle Roaring Fork  Valley Area, Pitkin County, Colorado. Report prepared for Pitkin County Board of County Commissioners by HSA and HHI.

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