The Effects of Vegetation Loss on the Two Elk Creek Watershed as a Result of the Proposed Vail Category III Ski Area Development CE 394 K.2 By Dave Anderson

The Effects of Vegetation Loss on the Two Elk Creek Watershed as a Result of the Proposed

Vail Category III Ski Area Development

CE 394 K.2

By Dave Anderson

The Effects of Vegetation Loss on the Two Elk Creek Watershed as a Result of the Proposed Vail Category III Ski Area Development

• Introduction and Background

• Development of the Two Elk Creek Watershed Using ArcView

• Determination of Annual Run-off

• Comparison of Results

• Conclusions


In 1985, Vail Associates, Inc. contacted the United States Department of Agriculture – Forest Service (Forest Service) and proposed to develop 4,100 acres of the Category III (CAT III) and Tea Cup Bowl areas on the White River National Forest

– Four development scenarios developed

– One out of four was “Proposed Alternative”

– Proposed Alternative included:

• Construction of four ski lifts• Ski Trails• Ski/Roadway System• Restaurant• Two Warming Shelters and Food Service Facilities• Ski Patrol Facilities• Utilities• Three small bridges spanning Two Elk Creek

Background


• The Forest Service accepted this Master Development Plan in a 1986 Decision Notice

• The DN withheld approval of the development of the CAT III area pending the completion of a site specific Environmental Impact Statement (EIS)

• The final EIS was completed in August 1996.

• It is possible that significant loss of vegetation in the CAT III area will occur if the EIS is approved

• This will affect the quantity and quality of surface (and ground) water in the immediate area


• Completed using:– Digital Elevation Models

• Downloaded from USGS Web Site

– River Reach Data• Downloaded from EPA Web Site

– Hydrologic Unit Data• Downloaded from EPA Web Site

– CRWR Pre-Processing Tools

Development of the Two Elk Creek Watershed

Leadville-e DEM

Leadville-w DEM• Steps Included:

– Import individual DEMs (3-arc second, 1:250,000 scale) into ArcView (Leadville, CO)

– Combine 2 DEMs using Mosaic function of CRWR Raster

– Project DEMs using ArcInfo• DEMs originally in Geographic Coordinates• Projected using Albers Equal-Area Method

LeadAlb DEM


• Steps Included (cont.):– Identify appropriate Hydrologic Unit (HUC) using EPA

Surf Your Watershed Web Site– Import shapefile for HUC 14010003 (Eagle County,

CO) into ArcView

State of Colorado

Upper Colorado River Basin Hydrologic Units

HUC of Interest

• Steps Included (cont.):– Mask Grid for HUC shapefile onto projected DEM to

obtain DEM for HUC– Import River Reach shapefile Into ArcView


• Steps Included (cont.):– Ran CRWR Preprocessor Tools to Delineate

Watersheds in Order to locate Two Elk Creek Watershed

• Steps Included (cont.):– Vectorized Streams and Watersheds to Determine Extent of

Two Elk Creek Watershed– Merged sub-watersheds within Two Elk Creek Watershed

Two Elk Creek Watershed


• Completed using:– Historical Annual Precipitation Data

• Downloaded from Oregon State University Web Site• Data from 1961-1990

– State Soil Geographic (STATSGO) Data• Downloaded from NRCS Web Site

– Land Use/Land Cover Data• Downloaded from USGS Web Site

– Look-up tables and avenue scripts provided by Dr. Maidment and CRWR

Determination of Annual Run-off

• Steps Included:– Import and project (Albers Equal-Area) annual

precipitation data• Data provided in contour format• Converted to grid format using avenue script written

by Andrew Romanek

– Develop grid for Two Elk Creek watershed• Masking precipitation grid with other grids previously

developed


• Steps Included (cont..):– Import STATSGO soil data for coverage of entire State

of Colorado

• Steps Included (cont..):– Import Land Use/Land Coverage data for coverage of

two Leadville DEMs previously shown


These STATSGO tables were combined to generate a table that presents the percentages of each soil group in a particular Map Unit...


Muidjoin.dbf was then combined with the look-up table (Rcn.txt) and the attributes of the land use table to generate a Curve Number grid...


With the Curve Number in each cell known, the annual runoff grid was calculated using the following equations:

S = 1000/CN -10 (Storage in inches)

(P-0.2S)2 (Runoff in inches)

P+0.8SQ =

The total annual runoff for the Two Elk Creek Watershed was calculated by summing the annual runoff in each cell within the limits of the watershed to produce the runoff grid.


To determine the impact of development on the Two Elk Creek Watershed, the percentage of each hydrologic soil group (A, B, C, and D) in the study area was changed based on estimates of acreage disturbed during development for the Proposed Alternative (as listed in the EIS). The original values appear to the right; the new values appear below.

The percentage of Group D soils was increased due to the existence of shallow soils underlain by a hard granite layer, and the construction of other impervious surfaces.

The total annual runoff for the Two Elk Creek Watershed was then re-calculated using the same method described previously.


• The results of the annual runoff calculation were compared to the values presented in the EIS for:

– Existing Situation (no development of CAT III area)– Proposed Alternative (development of select areas of the

Two Elk Creek Watershed

Comparison of Results

Area Dist. from top of watershed Mean Annual Existing Annual Proposed Alternative % Increase(acres) to Outlet (miles) Precipitation (in) Runoff (acre-ft/yr) Annual Runoff (acre-ft/yr) over Baseline

EIS 6645 4 35 8600 8683 0.01%ArcView 7066 4.28 27.69 14113 14338 1.59%% Difference 6.3% 7.0% 26.4% 64.1% 65.1% n/a

Comparison of Hydrologic Characteristics of Two-Elk Creek Watershed

Source

• Large discrepancies can be seen in mean annual precipitation and existing annual runoff

• A comparison of the runoff grids is provided below


• The effects of vegetation loss in comparison to the variability of annual runoff between the calculations in the EIS and those performed in ArcView is negligible.

• Two Elk Creek Watershed may be too small to effectively model with 3-arc second DEMs

– Discrepancies in sub-watershed areas due to resolution

– Soil data coverage too coarse to cover sub-basin changes in soil types

– Land Use/Land Cover data more detailed than soil data

• Although there are significant errors when compared to the EIS text, the data needed to make a runoff analysis such as this is available now or in the near future

Conclusions


Questions?

Documents

The Effects of Vegetation Loss on the Two Elk Creek Watershed as a Result of the Proposed Vail Category III Ski Area Development CE 394 K.2 By Dave Anderson