Black Lakes

Contour mapping of the Black LakesThe Black Lakes are located in the headwaters of Black Gore Creek near the summit of Vail Pass. Presently, water stored in the two reservoirs is used for a variety of purposes including snowmaking at Vail Ski Resort, augmentation for the Town of Vail, and on-site fishery and recreational uses. Resource Engineering, Inc. (RESOURCE) was hired by the Eagle River Water and Sanitation District (ERWSD) to complete a depth survey of Black Lakes No. 1 and No. 2. The purpose of the survey was to provide a highly accurate elevation-capacity and elevation-surface area description of the lakes and to provide an estimate of reservoir capacity loss, if any, due to sedimentation.

Staff conducting measurements on siteRESOURCE’s depth survey of the Black Lakes was conducted by continuously gathering depth information with an Echo-sounder Sonar system. Each depth reading was given a precise two-dimensional position with Global Positioning System (GPS) technology. The GPS and Sonar systems were mounted on a customized Cataboat. The system maintained an automatic log of position and depth while traveling over the water surface. Precise spatial locations were obtained during the survey by utilizing a Trimble GPS receiver. All GPS positions were differentially corrected via post-processing with high-accuracy GPS base-station data from the NOAA-CORS network. The spatial positions recorded with the GPS unit were paired with depth soundings provided by a sonar echo-sounder instrument. During the course of the survey, over 20,000 depth data points were collected.

RESOURCE used GIS software to process the reservoir survey data. The raw pairings of GPS spatial and Sonar depth data were converted to a high-resolution depth grid dataset. These grid datasets was interpolated into depth contours that describe the lake-bottom topography of both of the Lakes.

RESOURCE sought to identify and quantify sediment accumulation in the Black Lakes by comparing the contours that were developed during the survey to depth contours contained in the original surveys for the Black Lakes. By comparing these two sets of data in GIS, RESOURCE was able to identify zones of sediment accumulation. Further analysis in GIS allowed RESOURCE to quantify the volume of material contained in the zones of sediment accumulation. The volume of accumulated sediment directly reduces the available storage capacity in the Black Lakes.