Wadeable stream habitat monitoring at Ocmulgee Mounds National Historical Park: 2019 Change Report

Bateman McDonald, Jacob

doi:10.36967/nrr-2280071

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, Kennesaw Mountain National Battlefield, Ocmulgee Mounds National Historical Park, Chattahoochee River National Recreation Area, and Congaree National Park. 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 2019). 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), • 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-channel and near-stream habitat on a reach of Walnut Creek (OCMU001). These data, along with in-office analysis of remotely-sensed geographic information system (GIS) data, are presented in a baseline report that describes and compares the watershed-, reach-, and transect-scale characteristics of this reach of Walnut Creek to similar-sized streams at Kennesaw Mountain National Battlefield Park and Chattahoochee National Recreation Area (Cooper et al. 2019). On May 8, 2019, OCMU001 was resurveyed to determine the amount and type of change that occurred within the reach. This report compares the results of the 2019 resurvey to the initial 2017 baseline survey. Walnut Creek’s watershed at OCMU001 has low slope/relief and is covered mostly by forest and agricultural pasture. The major defining characteristics of the stream are the presence of floodplains and natural levees, the lack of riffle habitat, and a homogeneous channel slope throughout the reach. n-stream habitat changed substantially from 2017 to 2019. In 2019, only a few non-run habitats were identified within the reach (there was a mixture of runs and pools in 2017). Related to the conversion of pools to runs, thalweg depth was shallower in 2019 compared to 2017. Bed material was also finer in 2019 compared to 2017. Additionally, the floodplain surfaces along detailed transects 2 (T6) and 3 (T11) had a significant amount of aggradation. Floodplain aggradation on detailed transects 2 (T6) and 3 (T11), along with the overall shallowing of average thalweg depth within the reach, indicates a substantial amount of sediment is being supplied to the reach. Due to the reduction in the diversity of in-stream habitat and the increased fining of the bed, OCMU001’s in-stream habitat’s classification was downgraded from ‘poor to fair; to ‘poor.’ This classification is a generalized interpretation 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. The reduction in the quality of the habitat may be a ‘natural’ fluctuation within the stream network related more to complex response (Schumm 1973) than a permanent change in the reach. The lack of change in the longitudinal profile supports the interpretation that the reach has not undergone a significant permanent change and the additional fine sediment that has been deposited within the reach may move through this...

Wadeable stream habitat monitoring at Ocmulgee Mounds National Historical Park: 2019 Change Report

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