Effects of construction-related land use change on streamflow and sediment yield.

Observations from four small watersheds by the Reedy River in upstate South Carolina, USA, were used to evaluate the effects of urban development due to residential construction on streamflow and sediment yield, and to assess the effectiveness of Best Management Practices (BMPs). Paired watershed studies were used to quantify changes in flow magnitudes and sediment outputs at the watershed scale. A novel method based on the Revised Universal Soil Loss Equation was developed to quantify the contribution from each land use to watershed sediment yield. Area-normalized stormflows and peak flows in developed watersheds were 2-9 times greater than those from an undeveloped reference watershed. Sediment yield (SY) and event mean concentration (EMC) were 6 times greater in a developed watershed that had no ongoing construction. In actively developing watersheds, however, SY and EMC were 60-90 times greater compared to the reference. Sediment contribution factor (10 kg h MJ mm), defined as SY per unit rainfall erosivity, for each land use with 95% confidence interval was: Forest = 4 ± 2, Pasture = 2 ± 2, Full Development = 18 ± 11, Active Development = 440 ± 120. These values can be used to predict long-term change in sediment yield due to a future land-use change. Significant increases in flow and sediment occurred despite the use of BMPs, so improvements to their implementation and/or proper maintenance may be necessary to ensure that their protective goals are met.