Wadeable stream habitat monitoring at Ocmulgee Mounds National Historical Park: 2017 baseline report

Cooper, Christopher; McDonald, Jacob; Starkey, Eric

doi:10.36967/2268263

The Southeast Coast Network (SECN) stream habitat monitoring protocol collects data to give park resource managers insight into the status of and trends in stream and near-channel habitat conditions (McDonald et al. 2018a). Wadeable stream assessments are currently implemented at the five SECN inland parks with wadeable streams. These parks include Horseshoe Bend National Military Park (HOBE), Kennesaw Mountain National Battlefield (KEMO), Ocmulgee Mounds National Historical Park (OCMU), Chattahoochee River National Recreation Area (CHAT), and Congaree National Park (CONG). Streams chosen for assessment were specifically targeted for management interest (e.g., trail erosion issues and upstream urban development) or to provide a context for similar-sized stream(s) within the park or network (McDonald and Starkey 2019a). The objectives of the SECN stream habitat monitoring protocol are to: • Determine status of upstream watershed characteristics (basin morphology) and trends in land cover that may affect stream habitat; • Determine the status of and trends in benthic and near-channel habitat in selected wadeable stream reaches (e.g., bed sediment, geomorphic channel units [GCUs], and large woody debris [LWD]); and • Determine the status of and trends in cross-sectional morphology, longitudinal gradient, and sinuosity of selected wadeable stream reaches. On September 27, 2017, data were collected at Ocmulgee Mounds National Historical Park (OCMU) to characterize the in- and near-channel habitat on a permanently monumented reach on Walnut Creek (OCMU001). These data, along with in-office analysis of remotely-sensed geographic information system (GIS) data, are presented in this report to describe and compare the watershed-, reach-, and transect-scale characteristics of OCMU001 to selected third-order streams at Chattahoochee River National Recreation Area (CHAT001 and CHAT013) and Kennesaw Mountain National Battlefield Park (KEMO001 and KEMO002). Reach OCMU001’s watershed (Walnut Creek) has low slope/relief and is covered mostly by forest and agricultural pasture. The major defining characteristics of the stream were the presence of floodplains, natural levees, lack of riffle habitat, and homogeneous channel slope throughout the reach. Though the majority of the watershed lies in the Appalachian Piedmont physiographic province, the OCMU001 reach of Walnut Creek lies in the Upper Coastal Plain and is a low energy, depositional environment which is subject to regular flooding and slow post-flood draining. The channel surveyed at OCMU001 is smaller than expected, given the large size of its watershed. The small channel size is interpreted as evidence that the majority of flood waters that come through Ocmulgee Mounds NHP by way of Walnut Creek do not follow this flow path. Alternatively, flood waters are diverted away from the hillslope, into the wetlands to the west of OCMU001 and into a power line right-of-way east of OCMU001, through a series of flood chutes and side channels. It is suggested that discharge monitoring stations be installed at the railroad bridge that crosses Walnut Creek (upstream of OCMU001), just upstream of OCMU001, and immediately downstream of OCMU001 to determine the proportion of flow that bypasses the channel at OCMU001 and to determine how much floodwater enters OCMU001 through flood chutes and side channels. Though the reach had a high abundance of large woody debris (LWD), based on the results of the pebble count and the type/distribution of the geomorphic channel unit (GCU) within the reach, in-stream habitat within the surveyed stream was classified as “poor to fair.” These classifications are generalized interpretations of in-stream habitat and additional work is needed to determine how flow (e.g., flashiness of flow and baseflow conditions), water quality, and in-stream physical characteristics affect biodiversity and stream health at Ocmulgee Mounds NHP. Given the complex hydrologic setting of OCMU

Wadeable stream habitat monitoring at Ocmulgee Mounds National Historical Park: 2017 baseline report

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