Quantifying future changes in extreme events and associated flooding is challenging yet fundamental for stormwater managers. Along the U.S. Atlantic Coast, Eastern North Carolina (ENC) is frequently exposed to catastrophic floods from extreme rainfall that is typically associated with tropical cyclones. This study presents a novel approach that uses rainfall data from five dynamically and statistically downscaled (DD and SD) global climate models under two scenarios to visualize a potential future extent of flooding in ENC. Here, we use DD data (at 36-km grid spacing) to compute future changes in precipitation intensity–duration–frequency (PIDF) curves at the end of the 21st century. These PIDF curves are further applied to observed rainfall from Hurricane Matthew—a landfalling storm that created widespread flooding across ENC in 2016—to project versions of “Matthew 2100” that reflect changes in extreme precipitation under those scenarios. Each Matthew-2100 rainfall distribution was then used in hydrologic models (HEC-HMS and HEC-RAS) to simulate “2100” discharges and flooding extents in the Neuse River Basin (4686 km2) in ENC. The results show that DD datasets better represented historical changes in extreme rainfall than SD datasets. The projected changes in ENC rainfall (up to 112%) exceed values published for the U.S. but do not exceed historical values. The peak discharges for Matthew-2100 could increase by 23–69%, with 0.4–3 m increases in water surface elevation and 8–57% increases in flooded area. The projected increases in flooding would threaten people, ecosystems, agriculture, infrastructure, and the economy throughout ENC.

Recent hurricane and tropical storm-induced extreme rainfall events have caused hundreds of culvert washouts across North Carolina. These failures present serious vulnerabilities in the transportation network and pose a safety risk. As part of this study, the North Carolina Department of Transportation provided records for 1410 locations where hydraulic structures were reported to have washed out during Hurricanes Matthew and Florence and during extreme flooding in 2020. These records were analyzed to characterize the pre-storm properties of the structures and to identify factors that indicate high washout risk based on a remote desktop analysis. Drainage area, watershed characteristics, structure capacity, and physical parameters were calculated and compiled for all washouts. The same data were also compiled for nearby structures that did not wash out in a six-county area. Results indicated washouts were most common in small watersheds (0.5 mi 2 [<1.3 km 2 ]), for secondary roads, and for corrugated metal and reinforced concrete culverts with diameters of <72 in. (1.8 m). While the analysis did not reveal any specific parameters or thresholds that definitively predicted a washout would occur, several factors that appear to increase the potential were identified, including absence of a headwall, high headwater over culvert diameter ratios, and lower culvert cross-sectional area to watershed area ratios. We recommend agencies conduct asset inventories and inspections to document existing conditions, identify structures in poor condition or those that are very under-sized, and implement repair and upgrade efforts to help reduce failure risk.

Highlights Exclusion of beef cattle from two streams resulted in significant reductions in nitrogen, phosphorus, and sediment exports. Reductions in nutrient and sediment export improved following four or more years of exclusion. Nitrogen and phosphorus concentrations in storm samples decreased more than those in baseflow samples. Abstract. Fences were installed to exclude cattle from two adjacent small streams on a beef and swine farm located in central North Carolina. The two streams, referred to as UTA and North, originated in a pasture used for beef cow production and the application of swine waste. Rainfall and discharge were continuously monitored for 1.34 years prior to and 1.8 years after the fencing was installed in order to quantify the effect of the livestock exclusion on pollutant export/loads in the two streams originating in the pasture. Monitoring results documented reductions in total nitrogen (TN), phosphorus (TP), and total suspended solids (TSS) exports via the North stream of 15%, 54%, and 67%, respectively. Monitoring on the UTA stream was restarted 3.7 years after the initial 1.8 years and continued for about 1 year to assess the effect of natural vegetation growth and stream channel soil recovery. The combined reductions for the two periods were 39%, 64%, and 74% for TN, TP, and TSS, respectively. Exports of TN, TP, and TSS during the later monitoring period decreased by 13%, 60%, and 22%, respectively, compared to the initial 1.8-year monitoring period. These results indicated that exclusion fencing was effective at reducing pollutant exports during the first 1.8 years and that its effectiveness increased after about four years. Consequently, studies that report effectiveness during the first 2 to 4 years after exclusion likely underestimate the long-term effectiveness of the exclusion fencing. Keywords: Best management practices, Discharge monitoring, Livestock exclusion.

Phosphorus (P) budgets can be useful tools for understanding nutrient cycling and quantifying the effectiveness of nutrient management planning and policies; however, uncertainties in agricultural nutrient budgets are not often quantitatively assessed. The objective of this study was to evaluate uncertainty in P fluxes (fertilizer/manure application, atmospheric deposition, irrigation, crop removal, surface runoff, and leachate) and the propagation of these uncertainties to annual P budgets. Data from 56 cropping systems in the P-FLUX database, which spans diverse rotations and landscapes across the United States and Canada, were evaluated. Results showed that across cropping systems, average annual P budget was 22.4 kg P ha(-1) (range = -32.7 to 340.6 kg P ha(-1)), with an average uncertainty of 13.1 kg P ha(-1) (range = 1.0-87.1 kg P ha(-1)). Fertilizer/manure application and crop removal were the largest P fluxes across cropping systems and, as a result, accounted for the largest fraction of uncertainty in annual budgets (61% and 37%, respectively). Remaining fluxes individually accounted for <2% of the budget uncertainty. Uncertainties were large enough that determining whether P was increasing, decreasing, or not changing was inconclusive in 39% of the budgets evaluated. Findings indicate that more careful and/or direct measurements of inputs, outputs, and stocks are needed. Recommendations for minimizing uncertainty in P budgets based on the results of the study were developed. Quantifying, communicating, and constraining uncertainty in budgets among production systems and multiple geographies is critical for engaging stakeholders, developing local and national strategies for P reduction, and informing policy.

As the frequency of more intense storms increases and concerns grow regarding the use of dams and levees, the focus has shifted to natural infrastructure (NI) for flood mitigation. NI has shown some success at small scales; however, little work has been carried out at the large watershed scale during extreme events. Three NI measures (afforestation, water farming, and flood control wetlands) were evaluated in the Neuse River Basin of eastern North Carolina. Detailed geospatial opportunity and hydrologic modeling of the measures were conducted in three subwatersheds of the basin and results were extrapolated to other subwatersheds. NI opportunity was greater and associated modeled peak flow reductions were larger for two subwatersheds located in the lower portion of the basin, where there is less development and flatter land slopes. Peak flow reductions varied spatially depending on the type and placement of NI combined with the hydraulic and morphologic characteristics of the stream network. Extrapolation of reductions to other subwatersheds produced a 4.4% reduction in peak flow for the 100 year storm at the outlet of the river basin in Kinston as a result of water farming on 1.1%, wetlands controlling runoff from 5.7%, and afforestation of 8.4% of the river basin.

Natural infrastructure as a mitigation measure for flooding has received increased attention following recent extreme rainfall and flood events in North Carolina. While natural infrastructure (e.g., wetlands, floodplain expansion, reforestation, etc.) has been shown to reduce runoff and mitigate peak flows, it is difficult to predict the aggregate impacts of widespread implementation at the watershed scale for a given location. The primary objectives of this study were to identify suitable areas for natural infrastructure implementation on the landscape to reduce flooding and to use the Soil & Water Assessment Tool (SWAT) model to simulate the flood reduction and water quality impacts for three subwatersheds (~150 sq. km each) of the Neuse River Basin. Model results indicated that substantial localized annual maximum flow reduction (up to 30–40%) was possible, mostly correlated to the area of natural infrastructure implementation in the subbasin, but flood reduction benefits declined at the subwatershed-scale (1–16%). On a per hectare basis, wetlands sized and designed strategically for flood control had a greater impact on peak flow reduction than reforestation. The implementation of reforestation and flood control wetlands produced substantial nutrient and sediment load reductions, which also correlated with the area of natural infrastructure implementation. Total nitrogen load reduction ranged from 6 to 18% and total phosphorus load reductions from 4 to 17% for the most intensive implementation of wetlands restoration and reforestation. Sediment load reductions ranged from 16 to 30%. The results of this study illustrate that while flood reduction benefits can be realized at local scales (i.e., subbasin), a substantial area would need to be converted to natural infrastructure to provide flood reduction benefits at the watershed scale.

FloodWise is a pilot project that proposes innovative new approaches for flood disaster resilience by applying nature-based solutions (NBS) in Eastern North Carolina to control water runoff for brief periods after major storm events. We collected production and cost data from primary or secondary sources and used discounted cash flow and capital budgeting procedures at a 6% discount rate for NBS practices to estimate the amounts of payments necessary for farmland owners to break even to adopt NBS practices. Conventional crop farming was profitable already on suitable lands and served as the business as usual (BAU) case to compare to selected NBS practices. Warm-season pasture, loblolly pine forests and agroforestry, and no-till farming exceeded the 6% hurdle rate. Other conventional farm practices of hardpan breakup, cool-season pastures and trees, and bottomland hardwoods would require total payments of up to $600/acre to break even at 6%. Modifications of existing conservation practices, such as stream buffers, cover crops, silvopasture, and tile outlet terraces and tiling, fell in the second tier of total costs of up to $1,512/acre. Major NBS projects that required substantial earthmoving and flood control structures were more expensive - $3,734/acre for water farming (i.e., retention) with berms, $13,252/acre for a forest wetland bank, and about $88,000/acre for a major flood control wetland - and would displace most of the existing area for farm and forest management. However, larger floodwater structure projects could store more water for more extended periods; these storage quantities and benefits need to be assessed in future research.

Increased global temperatures resulting from anthropogenically induced climate changes have increased the frequency and severity of adverse weather events, including extreme rainfall events, floods, and droughts. In recent years, nature-based solutions (NBS) have been proposed to retain storm runoff temporarily and mitigate flood damages. These practices may help rural farm and forest lands to store runoff and reduce flooding on farms and downstream communities and could be incorporated into a conservation program to provide payments for these efforts, which would supplement traditional farm incomes. Despite their potential, there have been very few methodical assessments and detailed summaries of NBS to date. We identified and summarized potential flood reduction practices for the Coastal Plain of North Carolina. These include agricultural practices of (1) cover cropping/no-till farming; (2) hardpan breakup; (3) pine or (4) hardwood afforestation, and (5) agroforestry; establishing the wetland and stream practices of (6) grass and sedge wetlands and earthen retention structures, (7) forest wetland banks, and (8) stream channel restoration; and establishing new structural solutions of (9) dry dams and berms (water farming) and (10) tile drainage and water retention. These practices offer different water holding and storage capacities and costs. A mixture of practices at the farm and landscape level can be implemented for floodwater retention and attenuation and damage reduction, as well as for providing additional farm and forest ecosystem services.

Recent extreme rainfall events produced severe flooding across North Carolina's Coastal Plain, revealing deep vulnerabilities in many communities. Climate change is expected to exacerbate these problems by further increasing rainfall intensity and the frequency of extreme rainfall events. Due to the risks posed by these changing rainfall patterns, a shift in the approach to infrastructure planning and management is needed for many floodprone communities, particularly in regard to managing streams and floodplains in urban areas. This study proposes a framework for systematically evaluating stream restoration in combination with engineered improvements to culvert and bridge crossings to identify and optimize options for mitigating extreme events in urban areas. To illustrate the methodology, extensive hydraulic modeling was conducted to test four different strategies for reducing flooding along a channelized and armored stream, Big Ditch, located in Goldsboro, North Carolina, USA. The results indicate that neither floodplain restoration nor infrastructure modification alone could alleviate flooding along Big Ditch. Rather, a combination approach would be required to mitigate flooding, which could result in substantial benefits for storms in excess of the 100-year event. The results suggest that shifting to a multi-faceted approach to improve resiliency to extreme events could improve public safety and reduce future damages due to flooding.

A Bayesian total uncertainty analysis framework is presented to assess the model estimates of the effectiveness of watershed management practices in reducing nonpoint source (NPS) pollution. The framework entails a two-stage procedure. First, various sources of modeling uncertainties are characterized during the period before implementing Best Management Practices (BMPs). Second, the effectiveness of BMPs are probabilistically quantified during the post-BMP period. The framework was used to assess the uncertainties in effectiveness of two BMPs in reducing daily total nitrogen (TN) loads in a 54 ha agricultural watershed in North Carolina using the SWAT model. The results indicated that the modeling uncertainties in quantifying the effectiveness of selected BMPs were relatively large. Assessment of measured data uncertainty revealed that higher errors were observed in simulating TN loads during high flow events. The results of this study have important implications for decision-making under uncertainty when models are used for water quality simulation.

Nonpoint source (NPS) pollution originates from diffuse land areas that intermittently contribute pollutants to surface and groundwater. This article is a review of 1998 literature on several aspects of NPS pollution, including policy, economics, and management issues; effects and extent of pollutants in surface and groundwater; pollution controls; and modeling and monitoring. Increasingly NPS pollution reduction policy includes regulation. Parry (1998) explained the regulatory and nonregulatory programs developed by the U.S. Environmental Protection Agency (U.S. EPA) to control water pollution from agricultural sources of phosphorus. Programs discussed include the Clean Water Act's definition of confined animal feeding operations (CAFOs) as point sources, NPS program grants, the Coastal Zone Act Reauthorization Amendments of 1990; TMDLs, and the draft National Nutrient Overenrichment Assessment Strategy. More stringent controls of confined animal feeding operations were discussed in Christen (l998a), including U.S. EPA's Draft AFO Strategy; two congressional bills, particularly H.R. 3232 (The Farm Sustainability and Animal Feedlot Enforcement Act); and President Clinton's Clean Water Action Plan. Another article reported on Pennsylvania's Nutrient Management Act, which requires high-density livestock or poultry operations to develop and implement nutrient management plans (Christen, 1998b). Letson and Gollehon (1998) addressed the issue of manure management in times of increasing specialization, in places where animal production is separate from cropland. To assist policy-targeting efforts, the authors estimated the magnitudes and locations of manure and land for its treatment. This was done at the farm level rather than at the county level to avoid aggregation problems. Several articles evaluated environmental policies to control agricultural contamination. Livingston and Cory (1998) examined the current environmental policy governing nitrate contamination of groundwater in the South Platte alluvial aquifer in Colorado. The typical policy choice of best management practices (BMPs) was compared to optimal policy design, with recommendations presented for increased effectiveness of existing policy. Oenema and Roest (1998) discussed the pathways and controls of nitrogen and phosphorus losses to surface waters and presented estimates and predictions of the losses from agricultural soils to surface waters in The Netherlands before and after implementation of nutrient loss measures and policies. Falconer (1998) examined some of the problems of controlling pesticide contamination in Western Europe and the potential policy instruments for achieving pesticide use reduction for environmental improvement. Several articles discussed watershed-based permitting and total maximum daily loads (TMDLs). The U.S. EPA issued its Report of the Federal Advisory Committee on the Total Maximum Daily Load (TMDL) Program (U.S. EPA, 1998). Hun (1998) presented various viewpoints on the pros and cons of TMDLs, while Pelley (1998) discussed the challenges of developing and implementing TMDLs and presented examples of how states are implementing the program. Another article (Galya et a1., 1998) described watershed-based management and permitting, implications for discharg-

Quantifying the water quality benefits of conservation practices (BMPs) is prone to different types of uncertainties, a big portion of which stem from application of models. These uncertainties result in biased decisions when developing water quality trading programs. While trading ratios are currently applied mainly to account for the natural variability of nonpoint sources, they are rather applied as random safety factors without considering estimates of modelling uncertainties. A Bayesian total uncertainty analysis framework is presented to assess the model estimates of the effectiveness of BMPs in reducing nonpoint source pollution. The framework entails a two-stage procedure. First, various sources of modelling uncertainties are characterized during the period before implementing BMPs. Second, the effectiveness of BMPs are probabilistically quantified during the post-BMP period. The framework was used to assess the uncertainties in effectiveness of two BMPs in reducing daily total nitrogen (TN) loads in a 54 ha agricultural watershed in North Carolina using the SWAT model. The results indicated that the modelling uncertainties in quantifying the effectiveness of selected BMPs were relatively large. Assessment of measured data uncertainty revealed that higher errors were observed in simulating TN loads during high flow events. The results were used to develop bands of uncertainty around BMP efficiencies. Trading ratios were then determined using the cumulative probability distribution functions of TN loads from the nonpoint and point sources. The results of this study have important implications for decision-making under uncertainty when models are used for water quality simulation.

Reducing the export of nitrogen (N), phosphorus (P), and sediment from agricultural land in water-supply watersheds is a continuing goal in central North Carolina. The objective of this project was to document the effectiveness of a combination of livestock exclusion fencing and nutrient management implemented on a beef cattle pasture located in the Piedmont region of North Carolina. The quantity and quality of discharge from two predominantly pasture watersheds were monitored simultaneously for 3.8 yr before and after implementation of the exclusion fencing and nutrient management in the treatment watershed; a control watershed remained unchanged. The excluded stream corridor was intentionally minimized by constructing the fence line about 3 m from the top of the streambank on either side and limiting it to the main stream channel only. Monitoring included collecting flow-proportional samples during storm events and analyzing them for total Kjeldahl N (TKN), ammonia (NH-N), and inorganic (NO-N) N as well as total P (TP) and total suspended solids (TSS). Statistically significant reductions were observed in TKN (34%), NH-N (54%), TP (47%), and TSS (60%) loads in the treatment relative to the control watershed after fencing, whereas storm discharge and NO-N loads were not significantly different. These data show that even a relatively narrow exclusion corridor implemented on only the main stream channel can significantly reduce the export of N, P, and sediment from a beef cattle pasture.

Salmonella enterica is an important foodborne pathogen, and contamination of surface and ground water that may result from various human activities, such as animal production and urbanization, may contribute to the public health burden. The aims of this study was to determine the sources of Salmonella contamination in four different types of watersheds and to assess the relative contribution of multidrug-resistant strains. Eighty-six water samples collected from four different watershed systems, including those impacted by swine production (n = 12), residential/industrial (n = 34), crop agriculture (n = 12), and forestry (n = 28), were cultured for Salmonella and further characterized by serotyping, antimicrobial susceptibility testing, and pulsed-field gel electrophoresis genotyping. Salmonella prevalence was high in all four watersheds: residential/industrial area (58.8%), forestry (57.1%), crop agriculture (50%), and swine production (41.7%). Majority of the Salmonella isolates (87.1%) were pansusceptible. Multidrug resistance up to eight antimicrobials (R-type: AmStTeAxChCeKmGm) was detected in water samples that originated from swine production systems only. Serovars identified included Anatum, Gaminara, and Inverness (18.3% each) and Muenchen and Newport (8.7% each), Bredeny (7.6%), and Montevideo (6.8%). Pulsed-field gel electrophoresis analysis indicated genotypic relatedness among Salmonella recovered from residential/industrial and forestry-associated watersheds (genotypic cluster types A, C, D, E, F, G, H, and J), sites with relatively close geographic proximity. Swine-production-associated isolates were distinctly different from the others (genotypic cluster types B and I), corroborating the phenotypic findings. Overall, the findings suggest that all the various watersheds, including natural forest, remain important contributors of Salmonella contamination. While swine-production-associated water samples were not found to have a disproportionately high prevalence, it was the most important reservoir of multidrug-resistant strains.

Bioretention, a key structural practice of Low Impact Development (LID), has been proven to decrease peak flow rates and volumes, promote infiltration and evapotranspiration and improve water quality. Exactly how well bioretention mimics pre-development (or natural) hydrology is an important question that continues to be researched. Do bioretention outflow rates mirror shallow groundwater inter-event stream recharge flow associated with natural watersheds? Three small, undeveloped watersheds, located in the piedmont of central North Carolina, were chosen to represent natural hydrology. These watersheds ranged from 50 to 78ha and were comprised primarily of forest and pastureland. Each drained to a small stream, where flow rate was monitored for an extended period of time. Data collected from the natural watersheds was compared to outflow rates from four bioretention cells. The cells selected are located within the piedmont region and drain predominantly urban watersheds ranging from 0.2 to 0.9ha in size. Flow rates and cumulative volumes were determined for each site at the following intervals after stormflow/outflow began: 3, 6, 12, 18, 24, 30, 36, 42 and 48 hours. After normalizing the flow rates and volumes by watershed size, data were combined to form two data sets: bioretention outflow and stream inter-event flow. Nonparametric statistical analyses were performed on the datasets using the Wilcoxon signed rank test. Results indicate that there is no statistical difference between flow rates in streams draining undeveloped watersheds and bioretention outflow rates for the first 24 hours following the commencement of flow. Similarly, there is no statistical difference between the cumulative volumes released by the two systems during the 48 hours following the start of flow. These results indicate that bioretention cells behave comparably to natural, undeveloped conditions with respect to both flow rates and flow volumes and that bioretention outflows somewhat mirrow post storm event shallow groundwater recharge.

Low impact development (LID) stormwater practices are becoming more popular because of their ability to improve water quality and recharge groundwater. New regulations require water quality treatment of stormwater runoff in addition to reducing peak flows, especially in nutrient sensitive watersheds. Previously, the main focus of traditional stormwater practices had been on mitigating flooding and reducing peak flows; whereas, newer LID practices improve water quality and attempt to restore a site's natural or pre-developed hydrology. This is accomplished by promoting more evapotranspiration and infiltration. Three commercial shopping centers have been monitored from April 2008 to September 2009 to measure the performance of using LID stormwater treatment, traditional stormwater treatment, or no stormwater treatment. All three sites were monitored for water quality and hydrology, and they were located within 70-km of each other. The site with no stormwater treatment and the site with traditional stormwater treatment were located in Raleigh, NC, and the site with LID treatment was located in Nashville, NC. Since the sites did not receive the same precipitation depths for each storm, the hydrology data were normalized per area treated. The LID practices were designed to treat the first flush of runoff or water quality event. The LID site incorporated the use of bioretention, permeable concrete, and constructed wetlands. Seven bioretention cells of varying media depths (0.6-m and 0.9-m) treated the front asphalt parking lot, and permeable concrete treated the rear parking lot. Storage was added beneath the permeable concrete to completely capture a 2.5-cm event. The constructed wetlands treated rooftop runoff, miscellaneous paved areas, and outparcel lots. Each LID practice was monitored as a separate unit and the site was monitored as a whole system. Effluent was monitored from the retention basin at the site with traditional stormwater treatment. A mixture of parking lot and rooftop runoff was monitored at the site with no stormwater controls. In addition to the water quality and hydrology results, much was learned about the construction and implementation of multiple and large scale LID practices at one site. LID practices are typically more sensitive practices, so proper construction oversight, installation, and maintenance are vital to adequate functioning of these stormwater treatment devices. Errors at this site included: undersized bioretention cells, clogged bioretention cells, a continuously flowing bioretention cell due to interception of the water table, and constructed wetlands that remained flooded, resulting in vegetation die off.

Two grassed bioretention cells including internal storage zones (ISZs) were monitored for 16 months in central North Carolina. Each cell had a surface area of 106 m(2) and fill media depths were 0.75 and 1.05 m for the north (North) and the south (South) cells, respectively. Asphalt parking lot inflow and outflows were analyzed for nitrogen and phosphorus forms and fecal coliform (FC). Outflow volumes and peak flows for individual storms were generally less than those of inflow. Overall, except for NO2,3-N, effluent nitrogen species event mean concentrations (EMCs) and loads were significantly (alpha=0.05) lower than those of the inflow, and nitrogen species load reductions ranged from 47 to 88%. Apart from fall and winter, during which a longer hydraulic contact time seemed to be needed, the ISZs appeared to improve denitrification. Total phosphorus (TP) and OPO4-P EMCs were significantly lower than those of the inlet. Reductions were 58% (South) and 63% (North) for TP and 78% (North) and 74% (South) for OPO4-P. There was no significant difference in TP and OPO4-P loads between the inlet and the two outlets. Moreover, effluent concentrations for both phosphorus species were low, relative to other studies. The best nutrient EMC and load reductions occurred during the warm and humid seasons. When considering effluent concentrations in addition to removal rates, the grassed cells showed promising results for FC and nutrient pollution abatement when compared to conventionally vegetated bioretention (trees, shrubs, and mulch) previously studied in North Carolina.

16. Abstract This report summarizes the results of a water quality monitoring project to document the effects of the construction of the I40 bypass around Greensboro on the water quality of residential lakes in the Sedgefield and King’s Mill communities. This project was a continuation of the monitoring at 6 locations begun during HWY 200426. At each monitoring site, discharge was monitored continuously and samples of stream discharge collected on a flow-proportional basis throughout the project. All samples were analyzed for total suspended solids (TSS), total solids, and turbidity. A recording raingage was also maintained for all of the monitoring period in the Sedgefield lakes watershed and in-situ measurements of temperature, dissolved oxygen, conductivity, and pH were made periodically at each site. Monitoring data at all sites documented continued elevated sediment export and turbidity during the construction period as compared to the pre-construction period. The greatest increase in sediment export and turbidity occurred at the upstream site on the Tilly tributary. For this site, which was located just downstream of the highway corridor, a large percentage of the sediment load during the entire construction period was associated with two tropical storm systems that occurred in September 2004. At this time the highway was particularly susceptible to erosion because more than 20 ft of fill had recently been added to bring the road surface to near grade and the sideslopes were not vegetated yet. Increases in sediment loading and turbidity at the other sites during highway construction were less severe and more like what would be expected. Mean turbidity levels during construction at all sites downstream of highway construction were greater than 50 NTU. Limited monitoring of temperature, specific conductance, DO, and pH for all six sites showed that highway construction had little, if any, effect on these parameters, except possibly temperature, which appeared to increase at Tilly-up and King’s Mill-down, but this was not confirmed at the other sites. There were not enough samples analyzed to determine if the highway construction had any effect on nitrogen and phosphorus concentrations in discharge.