Effects of an Alpine Ski Resort on Hydrology and Water Quality in The
Total Page：16
File Type：pdf, Size：1020Kb
Effects of an Alpine Ski Resort on Hydrology and Water Quality in the Northeastern U.S.: Preliminary Findings from a Field Study Beverley Wemple1, Jamie Shanley2, and Jon Denner2, Don Ross3 1 Dept. of Geography and 3Dept. of Plant & Soil Science, University of Vermont, Burlington, VT 2 US Geological Survey, Montpelier, VT 3.5 200 Abstract Table 1: Comparison of of watershed characteristics (a) Q - West Branch Q - Ranch Brook 180 High elevation, forested watersheds are particularly vulnerable to stresses from development. Steep slopes 3.0 TSS - West Branch and thin soils rapidly transmit water, nutrients and sediment when disturbed by logging, road construction or West Branch Ranch Brook TSS - Ranch Brook 160 Cl - West Branch 2.5 other activities associated with development. The effects of forest harvesting practices on streamflowand 2 Cl - Ranch Brook 140 Watershed Area (km ) 11.7 9.6 ) -1 water quality in high-elevation, forested watersheds have been well studied and provide relevant information 120 about the susceptibility of these ecosystems to anthropogenic disturbance. Few studies have directly Watershed area in 2.0 · ski trails (%) 11.60 0.38 100 addressed the hydrologic or water quality effects of ski resort development on mountain streams, and these · West impervious surfaces* (%) 2.17 0.01 1.5 80 studies draw almost entirely from western U.S. examples. Ski resorts in the eastern U.S. face particular · exposed bedrock (%) 3.16 0.63 discharge (mm/hr) chloride (umoles/L x 10 development pressures. Transient and unpredictable snow conditions generate extensive need for total suspended solids (mg/L) Branch 1.0 60 snowmaking. Competitive economic pressure has motivated plans for slope-side village development and Land use Alpine skiing State forest, Nordic skiing 40 summer recreation facilities at many eastern U.S. ski resorts. 0.5 * includes buildings and paved or gravel roads and parking lots 20 Here, we report preliminary findings of a recently initiated paired-watershed study to examine the effects of # 0.0 0 alpine ski area development on water quantity and quality. Our study area is located on the eastern slope of 3/27/2001 4/3/2001 4/10/2001 4/17/2001 4/24/2001 5/1/2001 5/8/2001 5/15/2001 5/22/2001 Mt. Mansfield, Vermont, and includes the basins of Ranch Brook and West Branch (Figures 1, 2; Table 1). 2.5 40 100% (b) Ranch Brook is undeveloped, except for a network of cross-country ski trails and unsurfaced access roads, Q - West Branch and serves as our control watershed. West Branch encompasses nearly an entire major ski resort, with an Q - Ranch Brook 35 TSS - West Branch 80% 2.0 extensive network of alpine ski lifts and trails, day lodges, snowmaking facilities, and vacation homes. A TSS - Ranch Brook 30 major expansion of resort facilities and ski trails has recently received state approval. Our preliminary Ranch Cl - West Branch ) N Cl - Ranch Brook -1 # 60% 25 analysis indicates distinct differences in runoff and water quality between the two basins. Differences in basin 1.5 hydrographs suggest that ski trails alter the magnitude of runoff, particularly during spring snowmelt. Elevated Brook concentrations of total suspended solids in West Branch streamwater suggest that exposed surfaces (trails, 40% 20 West Branch 1.0 parking lots) may be important sources of sediment in the ski resort basin. Streamwater chemistry at West 1 0 1 discharge (mm/hr) 15 Ranch Brook 20% chloride (umoles/L x 10 % basin area below elevation Branch also indicates contamination by deicing salts. Variability in summer low flows between the two basins total suspended solids (mg/L) Kilometers indicates unexplained differences in precipitation capture or groundwater loss in the basins and must be 10 0.5 resolved in future analysis. These findings provide important baseline information for ski area management in 0% 5 the eastern U.S., where field studies have been sparse. Our future plans include hydrologic modeling to 0 200 400 600 800 1000 1200 1400 elevation (m) assess the effects of current development and various future development scenarios on streamflow and water 0.0 0 9/21/2002 9/22/2002 9/23/2002 9/24/2002 9/25/2002 9/26/2002 9/27/2002 9/28/2002 9/29/2002 quality. Figure 1: Study area Figure 2: Basin hypsometry Figure 3: Hydrographs and concentrations of total suspended solids and chloride for (a) spring snowmelt 2001 and (b) a summer storm in 2002. Hydrology Water Quality Conclusions Runoff analysis for the two basins indicates that flow is synchronized in time but distinctly different in peak Our preliminary data analysis indicates that development in the West Branch basin affects water quality. • Timing of runoff response is similar in the two basins with 80% of all paired peak flows occurring within one magnitude and water yield. In WY 2001 and 2002, 80% of all paired peak flow events occurred within 1 hour Concentrations of total suspended solids (TSS) are higher and are flushed earlier in West Branch compared to hour of each other. of each other at the two basins. Unit area peak discharge at West Branch is higher than at Ranch Brook for the Ranch Brook basin (Figure 3). TSS concentrations are related to discharge, but concentrations peak in summer and fall storms, but lower for winter and spring storms, suggesting that development increases peak advance of the runoff peak (Figure 3b), leading to considerable scatter in the TSS vs. discharge rating curve • Development appears to increase peak runoff for summer and fall storms but reduces peak runoff during runoff during rain events but reduces snowmelt peaks by storing and slowly releasing water from ski trails (Figure 7). Yield of TSS also varies seasonally, with higher concentrations in both basins during spring/summer snowmelt. (Figure 4). This seasonal difference is statistically significant (p = 0.04) in WY 2001, when prodigious natural storms, presumably due to the lack of snowcover protection. Deicing salts applied to ski area parking lots cause snow was available, but not in WY 2002 (p = 0.16), a drought year with little natural snowpack. Annual water a sharp chloride spike in streamwater at the onset of snowmelt (Figure 3a). The chloride concentration falls off • Sediment and chloride concentrations are higher in the developed basin, relative to the undeveloped basin. yield for WY 2001 at West Branch was over 40% higher than at Ranch Brook, and exceeds water yield at rapidly but the signal persists year round, remaining several times higher than at Ranch Brook in late summer other mountainous basins in the region (Figure 5). Differences in water yield between West Branch and storms (Figure 3b) • Water yield is 40% higher in the developed basin and exceeds annual water yield at other regional basins, Ranch Brook are larger than can be reasonably explained by land cover differences or basin hypsometry indicating unresolved differences in precipitation capture or groundwater contributions. (Figure 2, Table 1) and appear to be due to large differences in measured streamflow during low and moderate flow periods (Figure 6). We are currently investigating whether a high precipitation anomaly exists • Elevated chloride concentrations apparent in summer flows suggest an important groundwater contribution in in West Branch basin. West Branch. Water Yield 2001 WY Daily Flow Ratios (a) 4.0 (b) 4.0 (a) 10000 (b) 10000 50 3.0 Y = 0.95X + 0.24 Y = 0.99X + 0.25 1200 Ranch Brook R2 = 0.90 R2 = 0.91 West Branch 3.0 3.0 40 1000 2.5 1000 1000 Y = -0.42 + X 0.8 R2 = 0.35 Y = -0.14 + X 0.7 800 2.0 100 2.0 2.0 30 100 R2 = 0.22 600 20 1.5 Y = 0.72X + 0.35 10 10 Y = 0.69X + 0.14 2 2 runoff (in) West Branch Qp (mm/hr) 1.0 R = 0.96 West Branch Qp (mm/hr) 1.0 R = 0.79 400 runoff (mm) WY 2001 WY 2002 10 1.0 winter/spring winter/spring 200 1 1 Snowmaking total suspended solids (mg/l) total suspended solids (mg/l) winter/spring 0.0 summer/fall 0.0 summer/fall winter/spring 0.5 0.0 1.0 2.0 3.0 4.0 0.0 1.0 2.0 3.0 4.0 0 0 summer/fall summer/fall Flow ratio, West Branch / Ranch Ranch Brook Qp (mm/hr) Ranch Brook Qp (mm/hr) 0 0 west ranch pope dog ellis 0.0 1 10 100 1000 1 10 100 1000 10 20 30 40 50 60 Ranch Brook daily runoff, mm discharge (cfs) discharge (cfs) Figure 7: Scatterplots of total suspended solids vs. discharge at (a) Ranch Brook and (b) West Branch for WY 2001. Figure 4: Scatterplots of peak discharge at West Branch vs. Ranch Brook basin for (a) WY Figure 5: Annual water yield for WY 2001 at West Branch, Ranch Figure 6: Ratio of West Branch to Ranch Brook average daily Regression line is for all points (samples from winter/spring and summer/fall flows). The regression intercept is greater for 2001 and (b) WY 2002. Regression lines for seasonal effects are statistically different for WY Brook and three other basins in the region. Comparative basins flow vs. Ranch Brook average daily flow (WY 2001). West Branch than for Ranch Brook, suggesting slightly higher sediment yields in the managed basin; however, regression 2001 but not for WY 2002. Dotted line is 1:1. are Ellis River (USGS Station #01064300), Pope Brook (USGS lines for the two basins are not statistically different. Seasonal effects are statistically significant in both basins, indicating that Station #01135150), and Dog River (USGS Station #04287000).