Hydraulic Model Study of Little Falls Dam Fish Passage: Final Report
Alosa aestivalis, Alosa sapidissima, attraction, attraction flow, fish passage, flow patterns, habitat, herring, labyrinth weirs, Little Falls Dam, low head dams, migratory fish, model studies, perch, Potomac River, shad, spawning, swimming, Virginia, water depth, water velocity, weir
Little Falls Dam is located on the Potomac River. It stretches across the river between Maryland and Virginia and is about one mile upstream of Chain Bridge in Washington, D.C. This low head dam (approximately 12 feet high) was designed and constructed by the U.S. Army Corps of Engineers in 1959. As a feeder dam it provides water for the north of Virginia and the District of Columbia. The dam blocks access by migratory fish to ten miles of spawning and nursery habitat between Little Falls and Great Falls. A hydraulic model study was conducted to investigate the feasibility of notching the dam to provide attraction flow and adequate water depth for upstream fish passage of various species, including American shad (Alosa sapidissima), blueback herring (Alosa aestivalis), and white perch (Morone americana). A 1:8 scale 2-D model and 1:16 scale 3-D model were used to characterize water velocities and flow patterns. The range of river flow simulated was from 3,000 cfs to 30,000 cfs. Velocities within and downstream of the proposed notch were high (approximately 20 feet per second) and unsuitable for passage. Addition of labyrinth weirs and side slots reduced velocities below 12 feet per second, provided adequate depth for swimming, enhanced attraction flow and maintained positive flow downstream of the notch.