UVM Theses and Dissertations
Format:
Print
Author:
Zinni, Bethany Jane
Dept./Program:
Geology
Year:
2006
Degree:
MS
Abstract:
Identifying the paths by which precipitation moves through a mountain watershed is a challenging and important hydrologic topic in discussion today. The research described in this thesis involves a new application of well-documented watershed research methods. This work has rarely been applied to sites at the meso-scale before and therefore this work is a test of these methods under new conditions. Little is known about the effects of ski area development on hydrologic pathways. This research attempts to address this issue by examining the changes in a watershed following the expansion of a large-scale ski resort.
The meso-scale study sites used here are the Ranch Brook (9.6 krn²) and West Branch (11.7 km²) watersheds on the eastern side of Mt. Mansfield. The watersheds are similar in most aspects, the main difference being that Ranch Brook is undeveloped and West Branch encompasses a large-scale ski resort. A flow path analysis of these two watersheds was completed to determine if the same methods used in smaller watersheds, principal components analysis (PCA) and end-member mixing analysis (EMMA), are useful at a meso-scale. Event-level EMMA and hydrograph separations were also completed to determine trends in source water contributions through a hydrological event. The effect of ski resort expansion in one of the watersheds was then evaluated using these same methods.
These methods produced consistent results, identifying 3 to 4 source waters, which could account for up to 90% of the total variability in stream water. The relative importance of these source waters was dependent on season and they were different for the two sites; a deeper groundwater source contributes to flow in West Branch. In the summer, the strongest mixing relationships in the sites are between rain and deep groundwater, with distinct subsurface waters contributing under various conditions. In the winter, in Ranch Brook there is a dominance of shallower source waters likely due to the constant input of new water from snowmelt. This is not observed in West Branch due to the prevalence of the deeper groundwater source at that site.
Event-level analyses indicated that source waters contribute to flow in a shallowing-up sequence through events and also clearly indicate that antecedent conditions play a strong role in determining the relative contributions of pre-event and event water to storm flow in meso-scale sites. The expansion of a ski resort in one of the sites during the course of this work appears to have resulted in both temporary solute flushes and has potentially caused event water to follow a shallower flow path, possibly as a result of run-off from impervious areas. More work will be necessary to fully address the impacts of ski resort expansion on watersheds.
The meso-scale study sites used here are the Ranch Brook (9.6 krn²) and West Branch (11.7 km²) watersheds on the eastern side of Mt. Mansfield. The watersheds are similar in most aspects, the main difference being that Ranch Brook is undeveloped and West Branch encompasses a large-scale ski resort. A flow path analysis of these two watersheds was completed to determine if the same methods used in smaller watersheds, principal components analysis (PCA) and end-member mixing analysis (EMMA), are useful at a meso-scale. Event-level EMMA and hydrograph separations were also completed to determine trends in source water contributions through a hydrological event. The effect of ski resort expansion in one of the watersheds was then evaluated using these same methods.
These methods produced consistent results, identifying 3 to 4 source waters, which could account for up to 90% of the total variability in stream water. The relative importance of these source waters was dependent on season and they were different for the two sites; a deeper groundwater source contributes to flow in West Branch. In the summer, the strongest mixing relationships in the sites are between rain and deep groundwater, with distinct subsurface waters contributing under various conditions. In the winter, in Ranch Brook there is a dominance of shallower source waters likely due to the constant input of new water from snowmelt. This is not observed in West Branch due to the prevalence of the deeper groundwater source at that site.
Event-level analyses indicated that source waters contribute to flow in a shallowing-up sequence through events and also clearly indicate that antecedent conditions play a strong role in determining the relative contributions of pre-event and event water to storm flow in meso-scale sites. The expansion of a ski resort in one of the sites during the course of this work appears to have resulted in both temporary solute flushes and has potentially caused event water to follow a shallower flow path, possibly as a result of run-off from impervious areas. More work will be necessary to fully address the impacts of ski resort expansion on watersheds.