Benthic macroinvertebrate response to post-development stream hydrology and hydraulics

The relationships between benthic macroinvertebrate community health as measured by commonly used metrics and hydrologic and hydraulic variables were investigated on fifteen streams in the Ridge and Valley, Piedmont, and Coastal Plain provinces of northern Virginia. Differences in hydrological characteristics of the streams prior to and after watershed development were calculated using the Indicators of Hydrologic Alteration methodology and archived US Geological Survey daily stream flow data. Hydraulic characteristics of stream flow and morphology were modeled using the US Army's HEC-RAS hydraulic model using data gleaned from detailed topographic survey of the stream channels. Principal Component Analysis was used to identify significant associations between the independent hydrologic and hydraulic variables and the dependent biotic metrics.; PCA identified hydrologic indices of changes in flow predictability, minimum flows, and runoff flashiness, such as rise rate and fall rate, as most significantly related (P < 0.05) to benthic macroinvertebrate health. The hydraulic variables hydraulic radius, channel width divided by drainage area, Froude number, shear stress and stream power were also significantly related with macroinvertebrate community indices.; The results of the study suggest that future regulatory efforts aimed at protecting stream health might achieve the most efficient results by concentrating on measures that reduce the size and number of less-than-bankfull flows, in addition to current regulations aimed at shaving peak flows. Currently recognized measures in this vein include low-impact development strategies such as replacing conventional stormwater ponds with bio-retention, infiltration, and similar innovative approaches.