The effects of a catastrophic flood upon surface water and groundwater in southwestern New Hampshire
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Abstract
The surface water and groundwater effects of a severe rainstorm and resulting catastrqphic flood in a rural northern New England watershed were investigated in this study. After the fourth wettest July on record in southwestern New Hampshire, 23 ern of rain fell within a 24-hour period in a limited portion of the mountainous 285-km~ Cold River drainage basin. Rainfall intensity records for the state were broken as 15 cm of precipitation fell in two hours on August 7, 1986. The following day, an additional 8 cm fell.
This intense rainfall, well in excess of a 100-yr storm, caused severe flooding in the area, as water was unable to infiltrate thin soils and till due to the saturated antecedent moisture conditions. Major erosion occurred on hillsides as deep gullies were cut and alluvial fans of cobbles and boulders were deposited on the floodplain. The storm caused the flood of record on the ungaged Cold River, based on paleoflood indicators, and resulted in the deposit ion of a 24,700 m^2 (6-acre) delta, composed of cobble-size imbricated clasts, at the mouth of the river. A 2 m rise in the water level of a monitoring well at a landfill was noted following the storm illustrating the effect of secondary recharge from runoff over bedrock and saturated soils that supplemented primary recharge. Water level fluctuations in the well were correlated with rainfall and spring discharge over the study period, to help define recharge-discharge properties of the aquifer beneath the landfill.
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Thesis (M.A.)--Boston University
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