Publication Date

2017-4

Document Type

Honors Thesis

Degree Name

Bachelor of Arts

Department

Geosciences

Advisors

Robert Newton

Keywords

Geology, Hydrology, Dam, Reservoirs, Sediment accumulation, Mill River, Paradise Pond, Ponds-Massachusetts-Northampton, Dredging, Sediment transport, Mill River (Hampshire County, Mass.)

Abstract

The viability of sluicing sediment from a small impoundment during high flow events was investigated as an alternative to dry dredging. Paradise Pond (4 ha) is impounded by a 5m high dam on the Mill River in Northampton, Massachusetts. The pond is located 4km upstream of the confluence with the Connecticut River as well as a diversion channel that is part of a flood control system that protects the City of Northampton from flooding by the Mill River. A dam has been located at this site since the late 1600’s and for the past 50 years, accumulated sediment has been removed every 8-10 years by dry excavation. At least 17,000 m3 of sediment is removed each time in order to maintain the pond for recreational boating activity. Rising costs associated with disposing of dredge spoil, and concerns regarding downstream sediment starvation, make this option unsustainable. A new plan combines mechanical movement of sediment to the upstream side of the dam during a partial pond drawdown, with release of that sediment through the sluice gate at the bottom of the dam during high streamflow events. Releasing sediment to the downstream reach in this manner mimics the natural pattern of sediment transport through a fluvial system. A sediment transport model (MIKE 21 Curvilinear Modeling System by DHI) was used to evaluate the flow conditions under which sediment will be released through the sluice gate and move through the downstream reaches. The model was calibrated using data from a 100mm, 24hr rain event that occurred on September 30th 2015 that caused peak flow in the Mill River to exceed 3000cfs. This was the storm of record for 2015. The simulation demonstrates that sediment was not transported through the sluice gate during this event. Further simulations indicate that sluicing is more effective if sediment is manually transported to the channel just upstream of the dam. For the same size storm event, sediment is eroded from the area above the dam. Additionally, simulations of the downstream river section indicate that the sediment will not accumulate in the flood control channel.

Language

English

Comments

57 pages : color illustrations. Includes bibliographical references (pages 49-52)

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