Floodplain restoration with flood control: Fish habitat value of levee borrow pits

Abstract

Earthen flood control levees are often built using soil excavated from borrow pits lying parallel to and riverward of the finished levee. After construction, these pits can provide valuable floodplain habitats, and their value along corridors of larger rivers is well established. However, levee borrow pits along smaller streams have not been studied. Six waterside levee borrow pits were studied for about three years along Abiaca Creek, which drains a 202km2 watershed in central Mississippi. Fish were sampled annually from six pits using boat-mounted electrofishing, and water quality samples were collected weekly from four pits. Continuous records of stream and borrow pit water levels were coupled with topographic and bathymetric survey data of the floodway to compute the frequency of connection between each pit and temporal distributions of aquatic habitat characteristics. Pit water surface areas ranged from 0.4 to 11.7ha, and mean depth ranged from 0.5 to 1.8m. Pits were hydraulically connected to the stream 1–34% of the time. Dissolved oxygen concentrations ranged from 0.30 to 13.7mg/L and were inversely related to water depth. Fish collections yielded 1768 individuals representing 26 species. Larger-bodied fishes and some piscivores were more common in larger, more elongated pits with more sinuous shorelines and lower turbidity. Setback levees with waterside borrow pits are a viable stream corridor restoration concept for smaller streams as well as major rivers.