Degree Year

2014

Document Type

Thesis - Open Access

Degree Name

Bachelor of Arts

Department

Geology

Advisor(s)

Amanda Schmidt

Committee Member(s)

Dennis Hubbard
Jon Woodruff

Keywords

Tropical Storm Irene, Spring Flood of 1987, Flood control dams, Paleolimnology, Sediment

Abstract

Tropical Storm Irene hit the northeastern United States in August 2011 with impressive rates of precipitation and river discharge. However, it was the combination of this heavy rain with high antecedent soil moisture that made Irene so unusual. The Connecticut River had a particularly high sediment yield after the storm, with a sediment concentration over 1,000 mg/L at the mouth of the river. Littleville Lake on the Westfield River was selected as a study site because of its flood control feature, which allows for the calculation of trapping efficiency in dammed rivers. Coring in the lake showed that there was not much sediment to be found, Irene or otherwise. Nevertheless, the Irene sediment that was successfully collected proved to be anomalously grey, fine grained, low in organics, high in potassium and low in zirconium, which is consistent with previous observations. The high potassium concentration is consistent with the unweathered glacial tills in the upstream reaches of the watershed. The unweathered nature of the sediment suggests that Tropical Storm Irene crossed a threshold that allowed for the eroding of material at deeper depths. Deep source material that was instantly mobilized resulted in deposited sediment with very little weathering. This previously unexposed material is now at the surface and depositing in the reservoir about four times faster than before Irene. Furthermore, comparing Irene to the Spring Flood of 1987, an equally large event on the Connecticut River, we are able to conclude that not everywhere in the Connecticut River Watershed is affected by storms and floods in the same way. Comparisons in peak discharge between the Westfield, Deerfield and Connecticut watersheds show that floods due to large meltwater events do not hit the smaller western tributaries, such as the Westfield, as hard as the main trunk of the Connecticut River.

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