The Impact of Water Withdrawals on Summer Low Flows in the Ipswich River Watershed, MA, USA

Abstract:

The Impact of Water Withdrawals on Summer Low Flows in the Ipswich River Watershed, MA, USA

First Author: Bobyock

Second Author: Wollheim

Water use management can significantly impact watershed water budgets and the ecosystem services provided by flowing waters. The Ipswich River watershed located in north eastern Massachusetts has a history of unsustainable withdrawals and severe low summer flows, to the extent that the Ipswich river was at one point named one of the most endangered rivers in the nation. Although water withdrawals began to decline more steeply since 2008 to address the critical condition of the river, no studies have yet determined how the hydrology of the watershed has responded to reduced summer withdrawals. The question guiding this research is: How have summer low flows changed in the Ipswich R. Watershed in response to water use management over the last 80 years? This research primarily focused on historical data analysis from the past eight decades for metrics such as discharge, runoff, precipitation, runoff coefficient and withdrawals from sources such as the United States Geological Survey (USGS), the National Center for Environmental Information, local Town Public Works Departments, and the Ipswich River Watershed Association. The mean runoff ratio for each water withdrawal period was calculated (1939-1950 with low withdrawals, 1951-1970 with large water withdrawals, 1971-2008 with slowly increasing withdrawals, and 2008-2019 with decreasing withdrawals. We found that the average runoff ratio slightly increased as withdrawals increased over the entire time period of high withdrawals (~ 22% per decade) but increased more rapidly (~ 50%) when withdrawals were decreased in the most recent decade. As summer withdrawals declined, the summer runoff ratio and discharge slightly increased (p = 0.08. These results suggest that summer discharge is influenced by the withdrawals, and that flow conditions are improving since they declined, but that other factors like spring precipitation may also need to be considered to understand summer conditions.