Hydrology and water quality of Little Cross Creek, Cumberland County, North Carolina, 1996-98
Little Cross Creek is a small stream located in Cumberland County, North Carolina, in the Sand Hills area of the Coastal Plain Province. From August 1996 through August 1998, the U.S. Geological Survey collected streamflow, water-quality, and time-of-travel data at 10 sites in Little Cross Creek Basin to assess ambient conditions and compute loads of suspended sediment, total nitrogen, total phosphorus, and total organic carbon. Streamflows in the Little Cross Creek Basin responded to climatic factors and to human activities such as water withdrawals and controlled releases from impoundments. Peak streamflows were observed during the passages of Hurricane Fran in September 1996 and Hurricane Josephine in October 1996. Streamflows generally were lowest during the summer and early fall of 1997, reflecting drought conditions associated with a prevailing El Nino. At most sites, average streamflow per unit drainage area, or yield, was higher than yields reported previously for the Sand Hills. High yields may have resulted from unidentified inputs of water to the study basins or from underestimation of the contributing drainage area. Bonnie Doone Lake, Kornbow Lake, Mintz Pond, and Glenville Lake, four impoundments of Little Cross Creek, notably influence hydrology and water quality in the basin. Streamflow records indicate that these impoundments dampen peak stormflows and delay the downstream release of stormwater. Time of travel also is affected by seasonal stratification in the reservoirs. In general, sites downstream from reservoirs have lower concentrations of suspended sediment, turbidity, and total phosphorus than sites upstream from reservoirs or sites that receive stormwater runoff. Few water-quality problems were observed in the Little Cross Creek Basin for the constituents that were sampled. However, fecal coliform bacteria commonly exceeded 200 colonies per 100 milliliters at two of the seven monitored sites during the study. Relatively high concentrations of specific conductance, total phosphorus, and total ammonia plus organic nitrogen were observed in Clark Pond Creek, a tributary to Little Cross Creek. Loads and yields of suspended sediment, total nitrogen, total phosphorus, and total organic carbon were computed for the period from October 1996 through September 1997. The highest suspended-sediment yield (230 tons per square mile per year) occurred upstream from Bonnie Doone Lake, probably because there were no impoundments upstream from this site to intercept sediment. Sediment yields at the remaining Little Cross Creek sites were low relative to yields reported from other urban basins in North Carolina. Downstream from Kornbow Lake, yields of suspended sediment (9.50 tons per square mile per year) and total phosphorus (0.011 ton per square mile per year) were very low. Clark Pond Creek had the highest yields ot total phosphorus (0.081 ton per square mile per year) and total organic carbon (11.5 tons per square mile per year). However, total phosphorus yields at all of the Little Cross Creek sites generally were lower than yields measured in other urban basins in the State. Comparison of inflow and outflow loads for the four Little Cross Creek reservoirs from October 1996 through September 1997 indicated that Bonnie Doone Lake trapped 92 percent of incoming sediment and 37 percent of incoming total phosphorus. Kornbow Lake trapped 57 percent of incoming sediment and 77 percent of total phosphorus inputs. Nitrogen was not effectively trapped by any of the reservoirs. An influx of sediment, total phosphorus, and total organic carbon was noted at a site downstream from Mintz Pond, and may have resulted from stormwater discharge from the U.S. Highway 401 bypass or from additional, unidentified sources in the watershed downstream from Kornbow Lake.