Research about Difficult Run watershed

USGS2019

Valuation of the flood attenuation ecosystem service in Difficult Run, VA, USA

Floodplains and riparian wetlands provide several ecosystem services that directly benefit people. We present a methodology for valuing the flood attenuation ecosystem service in Difficult Run, a suburban watershed with extensive natural floodplains in northern Virginia. High-resolution lidar-derived data were combined with GIS modeling techniques to produce estimates of flood inundation. We combined the modeled estimates with parcel-level property and primary economic data using a baseline and a counterfactual scenario to estimate the magnitude of flood attenuation and the associated value of the ecosystem service. Our framework brings new models and data to look at floodplains and an alternative land surface scenario in a way that has not previously been done. Annualized avoided property losses totaled $42,184 in the baseline scenario and $115,596 in the counterfactual scenario for the combined 200-, 100-, 50-, 20-, 10-, and 5-year flood events. We estimate the total annualized value of the flood attenuation ecosystem service in Difficult Run is $73,412, which is $77 per hectare of floodplain area and is consistent with similar valuation studies of floodplains. The framework presented here is not specific to the study area and could be deployed at larger spatial areas in other locations. Our methods may better inform land use decision making on the impacts of development in and surrounding floodplain areas.

Virginia↗

USGS2017

Storms, channel changes, and a sediment budget for an urban-suburban stream, Difficult Run, Virginia, USA

Determining erosion and deposition rates in urban-suburban settings and how these processes are affected by large storms is important to understanding geomorphic processes in these landscapes. Sediment yields in the suburban and urban Upper Difficult Run are among the highest ever recorded in the Chesapeake Bay watershed, ranging from 161 to 376 Mg/km 2 /y. Erosion and deposition of streambanks, channel bed, and bars and deposition of floodplains were monitored between 1 March 2010 and 18 January 2013 in Upper Difficult Run, Virginia, USA. We documented the effects of two large storms, Tropical Storm Lee (September 2011), a 100-year event, and Super Storm Sandy (October 2012) a 5-year event, on channel erosion and deposition. Variability in erosion and deposition rates for all geomorphic features, temporally and spatially, are important conclusions of this study. Tropical Storm Lee was an erosive event, where erosion occurred on 82% of all streambanks and where 88% of streambanks that were aggrading before Tropical Storm Lee became erosional. Statistical analysis indicated that drainage area explains linear changes (cm/y) in eroding streambanks and that channel top width explains cross-sectional area changes (cm 2 /y) in eroding streambanks and floodplain deposition (mm/y). A quasi-sediment budget constructed for the study period using the streambanks, channel bed, channel bars, and floodplain measurements underestimated the measured suspended-sediment load by 61% (2130 Mg/y). Underestimation of the sediment load may be caused by measurement errors and to contributions from upland sediment sources, which were not measured but estimated at 36% of the gross input of sediment. Eroding streambanks contributed 42% of the gross input of sediment and accounted for 70% of the measured suspended-sediment load. Similar to other urban watersheds, the large percentage of impervious area in Difficult Run and direct runoff of precipitation leads to increased streamflow and streambank erosion. This study emphasizes the importance of streambanks in urban-suburban sediment budgets but also suggests that other sediment sources, such as upland sources, which were not measured in this study, can be an important source of sediment.

Virginia↗