Pitkin County - CSC GW GIS

Hydro(geo)logic Conceptualization and Development of GIS-Based Ground Water Resources Evaluation of the Capitol and Snowmass Creek Study Area, Pitkin County, Colorado

Purpose of study

Under an agreement with Pitkin County, Hydrologic Systems Analysis, LLC (HSA) of Golden, Colorado, in cooperation with Heath Hydrology, Inc. (HHI) of Boulder, Colorado, with assistance from Marieke Dechesne, Geologist/GIS Specialist, Boulder, Colorado, created a GIS-based ground water resources evaluation procedure for use as a decision/land use management tool by Pitkin County. The step-wise procedure, supported by GIS maps and associated databases, can be used to guide a site-specific qualitative analysis with respect to: 1) ground water resources availability (in terms of both quantity and economic exploitability); 2) long term sustainability of the water supply; and 3) the vulnerability of the water resources to contamination. In addition, the developed GIS maps and data bases includes information with respect to required ground water augmentation due to a well's potential impact in surface water resources. The GIS maps and databases cover the Capitol/Snowmass Creek (CSC) area and were developed to complement areas covered by previous studies conducted for Pitkin County by HSA/HHI, specifically, the development of a GIS-based ground water resources evaluation procedure for the & Upper and Middle Roaring Fork study.

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

In the absence of previous area-wide hydrogeologic studies for the Capitol/Snowmass Creek area, HSA/HHI performed a hydrologic systems analysis, resulting in conceptual hydrogeologic and hydrologic models and hydrogeologic GIS layers and data bases.  These new GIS layers and data bases were combined with GIS layers and databases from Pitkin County, Colorado Division of Water Resources/Colorado Water Conservation Board, and the Natural Resources Conservation Service (USDA) to facilitate the site-specific application of the ground water resources  evaluation procedure.

The GIS layers of the CSC 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).

Three case studies were developed to illustrate the analysis procedure, one in the lower Capitol Creek area, one in the Lime Creek area, and the third is on the ridge between upper Capitol Creek and upper Snowmass Creek. The case studies chosen show the existing uncertainties in evaluating local groundwater resources and illustrate the variability of drinking water supplies. All three sites were deemed 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., P.K.M. van der Heijde, and M. Dechesne. April 2007. GIS-Based Ground Water Resources Evaluation of the Capitol and Snowmass Creek (CSC) Study Areas, Pitkin County, Colorado. Report prepared for Pitkin County Board of County Commissioners by HSA and HHI.

For more information contact: info@heath-hydrology.com

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