Indicators of Hydrologic Alteration in North Carolina Catchments

Alterations to stream hydrology, which includes changes in stream geomorphology, are primary impacts of anthropogenic disruption. In North Carolina, hydrological alterations lead to environmental impacts through degraded ecosystems and water quality. In collaboration with the North Carolina Department of Environmental Quality, Division of Mitigation Services (DMS), the USGS South Atlantic Water Science Center datasets as proxy measurements of the extent of altered hydrology in riverine systems across the State. The datasets consists of an inventory and characterization of small scale, mostly agricultural ponds and artificial drainage which are a both significant hydrologic modifications in the region. Ponds are impoundments that have been used for flood control, water supply, irrigation and recreation. The constitute modifications to the stream network that fragment the aquatic habitat by limiting river network connectivity necessary for fish passage. A dataset was developed to quantify small ponds as proxy measures of barriers to flow in stream network across the State. The USGS used a combination of the 2016 National Land Cover Dataset and the National Hydrography Dataset to identify 135,366 dams that are less than 10 acres. The features are more refined than larger scale assessments such as those in the National Hydrologic Dataset (NHD) Plus High Res and provide a starting point for determining mitigation strategies. Artificial drainage has major ecosystem impacts through the development of extensive ditch networks that reduce storage and induce large-scale vegetation changes. This has been a widespread practice of water table management for agriculture in Eastern North Carolina. However, these features are challenging to identify and because of their structure has been determined by non-natural factors. A dataset of open ditches was processed by calculating terrain (also, positive) openness ? a value based a line-of-sight approach to measure the surrounding eight zenith angles as viewed above the landscape surface. The result from calculating openness with high resolution DEMs (LIDAR) was then refined by masking natural water ways (stream valleys) and channels that are associated with transportation and urban areas.