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 (10-2 kg h MJ-1 mm-1), defined as SY per unit rainfall erosivity, for each land use with 95% confidence interval was: Forest = 4 ±â€¯2, Pasture = 2 ±â€¯2, Full Development = 18 ±â€¯11, Active Development = 440 ±â€¯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.

Nutrient exports from watersheds with varying septic system densities in the North Carolina Piedmont.

Septic systems (SSs) have been shown to be a significant source of nitrogen and phosphorus to nutrient-sensitive coastal surface and groundwaters. However, few published studies have quantified the effects of SSs on nutrient inputs to water supply watersheds in the Piedmont region of the USA. This region consists of rolling hills at the surface underlain by clayey soils. There are nearly 1 million SSs in this region, which accounts for approximately 50% of all SSs in North Carolina. The goal of this study was to determine if significant differences in nutrient concentrations and exports exist between Piedmont watersheds with different densities of SSs. Water quality was assessed in watersheds with SSs (n = 11) and a sewer and a forested watershed, which were designated as controls. Stream flow and environmental readings were recorded and water samples were collected from the watersheds from January 2015-December 2016. Additional samples were collected from sand filter watersheds in April 2015-March 2016 to compare to septic and control watersheds. Samples were analyzed for total dissolved nitrogen (TDN) and orthophosphate (PO4-P). Results indicated that watersheds served by a high-density (HD) of SSs (4.9 kg-N yr-1 ha-1; 0.2 kg-P yr-1 ha-1) exported more than double the median masses of TDN and PO4-P, respectively, relative to low-density (1.0 kg-N yr-1 ha-1; <0.1 kg-P yr-1 ha-1) and control watersheds (1.4 kg-N yr-1 ha-1; <0.1 kg-P yr-1 ha-1) during baseflow. Isotopic analysis indicated that wastewater was the most likely source of nitrate-N in HD watersheds. In all other watersheds, isotopic results suggested non-wastewater sources as the dominant nitrate-N provider. These findings indicated that SS density was a significant factor in the delivery of septic-derived nutrients to these nutrient-sensitive, water supply watersheds of the North Carolina Piedmont.

Impact of Soil and Water Conservation Interventions on Watershed Runoff Response in a Tropical Humid Highland of Ethiopia.

Various soil and water conservation measures (SWC) have been widely implemented to reduce surface runoff in degraded and drought-prone watersheds. But little quantitative study has been done on to what extent such measures can reduce watershed-scale runoff, particularly from typical humid tropical highlands of Ethiopia. The overall goal of this study is to analyze the impact of SWC interventions on the runoff response by integrating field measurement with a hydrological CN model which gives a quantitative analysis future thought. Firstly, a paired-watershed approach was employed to quantify the relative difference in runoff response for the Kasiry (treated) and Akusty (untreated) watersheds. Secondly, a calibrated curve number hydrological modeling was applied to investigate the effect of various SWC management scenarios for the Kasiry watershed alone. The paired-watershed approach showed a distinct runoff response between the two watersheds however the effect of SWC measures was not clearly discerned being masked by other factors. On the other hand, the model predicts that, under the current SWC coverage at Kasiry, the seasonal runoff yield is being reduced by 5.2%. However, runoff yields from Kasiry watershed could be decreased by as much as 34% if soil bunds were installed on cultivated land and trenches were installed on grazing and plantation lands. In contrast, implementation of SWC measures on bush land and natural forest would have little effect on reducing runoff. The results on the magnitude of runoff reduction under optimal combinations of SWC measures and land use will support decision-makers in selection and promotion of valid management practices that are suited to particular biophysical niches in the tropical humid highlands of Ethiopia.

The selection of paired watersheds affects the assessment of wildfire hydrological impacts.

Wildfires strongly alter hydrological processes and surface and groundwater quality in forested environments. The paired-watershed method, consisting of comparing a burnt (altered) watershed with an unburnt (control) watershed, is commonly adopted in studies addressing the hydrological effects of wildfires. This approach requires a calibration period to assess the pre-perturbation differences and relationships between the control and the altered watershed. Unfortunately, in many studies, the calibration phase is lacking due to the unpredictability of wildfires and the large number of processes that should be investigated. So far, no information is available on the possible bias induced by the lack of the calibration period in the paired-watershed method when assessing the hydrological impacts of wildfires. Through a literature review, the consequences of the lack of calibration on the assessment of wildfire hydrological changes were evaluated, along with the most used watershed pairing strategies. The literature analysis showed that if calibration is lacking, misestimation of wildfire impacts is likely, particularly when addressing low-severity or long-term wildfire effects. The Euclidean distance based on physical descriptors (geology, morphology, vegetation) was proposed as a metric of watersheds similarity and tested in mountain watersheds in Central Italy. The Euclidean distance proved to be an effective metric for selecting the most similar watershed pairs. This work raises awareness of biases exerted by lacking calibration in paired-watershed studies and proposes a rigorous and objective methodology for future studies on the hydrological effects of wildfires.