John C Hayes

Impacts of Land Disturbance on Aquatic Ecosystem Health: Quantifying the Cascade of Events

ABSTRACT The impacts of land disturbance on streams have been studied extensively, but a quantitative mechanism of stream degradation is still lacking. Small changes in land use result in changes in physical and chemical characteristics in the stream, which significantly alter biotic integrity. The objective of this study was to quantify the mechanisms of aquatic ecosystem degradation in streams impacted by watershed urbanization. By quantifying the development level and the changes in the physical parameters of receiving streams, the effects of land use change can be illustrated in a conceptual model and evaluated using a traditional ecological risk assessment framework. Three 1st-order streams draining catchments undergoing varying stages of land development were examined in the upper Piedmont physiographic province of South Carolina, USA. A disturbance index was developed to quantify the changes in land use on a monthly basis. This normalized disturbance index (NDI) was quantitatively linked to an increase in the percentage of impervious cover, stormwater runoff, storm-event total suspended solid (TSS) concentrations, and the North Carolina biotic index (NCBI). The NDI was inversely related to a decline in habitat, median bed-sediment particle size, and benthic index of biotic integrity (BIBI). Unlike the percentage of impervious cover, the NDI facilitated the development of strategies for multiple scales of regulation. Predictive multivariate regressions were developed for storm-event TSS concentrations, the BIBI, and the NCBI. These regressions can be used to develop improved regulations for the effects of development and can lead to better implementation of best management practices, improved monitoring of land use change, and more sustainable development.

SEDPRO Modeling of BMP Effectiveness at Construction Sites

An overview of SEDPRO is given and used to illustrate impacts of changing land use on the environment during urban development. Its use is illustrated for selected watersheds within a rapidly developing area (Greenville County, SC, USA) Basic concepts and development of this innovative model are described to provide an understanding of the approach and limitations. Enhancements over the widely distributed SEDIMOT II and SEDIMOT III models include a graphical interface that features drag and drop placement of subwatersheds, best management practices (BMPs), and conveyances. This feature allows the user to place BMPs at points throughout the watershed and evaluate trapping efficiency of individual BMPs as well as the entire treatment train. Additional BMPs included are sand filters, bioswales, and engineered devices. It also can be used on any order watershed, not just the 3 rd order allowed in SEDIMOT. SEDPRO is used in the paper to illustrating the impact of alternative land uses and different types of construction.

Predicting Water Quantity and Quality Based on Estimated Development Within the Reedy River Watershed

With ever changing water quality regulations, continuing development of Greenville County, and the increased demand for our water resources, modeling the impacts that future development, and the pattern of that development, may have on the area is critical for preserving our water resources and for the economic health of the region. As the Upstate continues to develop, the negative effects that have been observed in the Reedy River Watershed will only increase. The objective of this study was to model and analyze the water quantity and quality impacts within the Reedy River Watershed from future growth.

Eroded Particle Size Distributions for Southeastern U.S. Soils

Sediment is a significant negative byproduct of construction sites, agriculture, mining, and other land disturbing operations. Recently renewed attention has been given to controlling construction-derived sediment loading to natural waters. Evaluation of sediment control systems usually involves models that require input for prediction of sediment transport and deposition; therefore it is important to obtain eroded size distributions (ESD). ESD is used in detachment equations and determining pond efficiencies. Currently recommended procedures for estimating eroded size distributions used in design of sediment control structures often revert to simplistic rule of thumb methods, primarily due to lack of a universally accepted method. Sediment ponds and other structures designed by such estimates may be oversized or undersized. Another recommended method is based upon equations to determine amounts of sand, silt, clay, and large and small aggregates. Percentages of each are then used to estimate an ESD. Much research has been done for primary particle size distributions. The basic process is to take a sample of soil and mix a solution of sodium hexamedaphosphate and water to disperse aggregates into primary particles. However, primary particle distributions are not what are needed for estimating sediment transport and deposition because aggregates are naturally present in sediment-laden runoff. The importance of ESD becomes evident in settling velocities and in the amount of force required to keep the particle in transport. Previously, equations were statistically produced from a limited number of soils and later improved to better predict the amount of eroded material. These equations are used in the CREAMS (Chemical, Runoff, and Erosion from Agricultural Management Systems) and other models. However, these equations have limited applicability because they were developed for agricultural soils with high clay content and organic matter. This paper compares methods based on the CREAMS equations with ESD obtained from a rainfall simulator in predicting ESD from soil textures in 17 southeastern U.S. topsoils and subsoils. Additionally, USDA Natural Resources Conservation Service soil surveys contain dispersed particle size data in the engineering section. These data were used to get average percent clay and sand as input for the CREAMS equations, and values are then interpolated for ESD. A standard hydrometer test was also performed on each soil sampled in this project. ESD was calculated in much the same way as the soil surveys, except texture is a direct result of the hydrometer test. In addition, impact of errors in eroded size distribution on trapping efficiency of sediment control structures will also be demonstrated.

Analysis of Escherichia coli within Sediment Basins on Active Construction Sites

The conventional method of controlling sediment-laden runoff on construction sites is the use of sediment basins. These basins slow the velocity of runoff and allow particles to settle from the water column before discharge to surface waters offsite. This best management practice, however, may create a reservoir for Escherichia coli. Sediment is known to provide protection for bacteria; therefore, while these basins decrease sediment loadings to water bodies downstream, they may introduce harmful levels of pathogenic bacteria into receiving waters. In addition to increasing risk to human health, high bacteria levels may alter natural biological complexity of downstream ecosystems.

Accuracy and Precision of Portable Turbidity Meters

EPA has published effluent limitations guidelines (ELGs) to control discharge of pollutants from construction sites. Numeric turbidity limits for construction site discharge are expected to be required in the near future. Such requirements will likely include subjecting construction site stormwater discharges to a maximum allowable turbidity numeric effluent limit in nephelometric turbidity units (NTUs) for sites disturbing 10 acres or more

Filtration and Sorption BMP Modeling for Water Quantity and Quality

Water quantity and quality models are presented for storm water BMPs that primarily filter sediment, chemicals, and bacteria. Included are models for bioretention cells, stormwater sand filters, infiltration trenches, and bioswales. These models speciate sediment into aggregates and primary particles classes with a size distribution within the each particle class; chemicals into particulates, sorbed, and dissolved; and bacteria into sorbed and planktonic (floaters). Trapping of each species is calculated using mathematical representations of physical and chemical based processes yielding outflow hydrographs, sedigraphs, chemigraphs, and bacteriagraphs. The impacts of chemical additives and clay particles on sorption of chemicals and bacteria is predicted along with impacts of mechanical filtration and settling. An example analyses of the impact of the ratio of BRC surface area to watershed are is given to illustrate that simple rules of thumb are questionable methods for designing LID BMPs.

Low Impact Development Decision-Making to Evaluate Impacts of BMP Selection

As upstate South Carolina continues to develop, stormwater runoff must be managed for its quantity and quality. Therefore, an incentive-based program to encourage developers to use low impact development (LID) designs is being developed for Greenville County. To achieve this goal, various best management practices (BMPs) were researched for their effectiveness and feasibility, and a post construction index (PCI) was developed to rate development. The PCI helps address questions about the benefit of small structures scattered around a development as compared to larger structures located near the outlet point and also considers economics of BMPs. The PCI is related to available parameters to scientifically anchor the PCI and make it directly related to stormwater runoff and water quality characteristics that reflect benefits of structural, non-structural, management and maintenance practices. The PCI is a function of nine (9) defined sub-factors with each having a range from zero to a maximum score of 5, 10, 15 or 20. Total scores for all sub-factors are used to differentiate between the water quality impacts of legacy, conventional, and innovative housing developments/LID designs.

Developing Stormwater Educational Programs for Rapidly Urbanizing Areas

Like many areas throughout the U.S., urban growth within South Carolina is occurring at a tremendous rate. As a result of environmental concerns, the Clemson University Cooperative Extension Service initiated public education programs in communities across the state. This presentation provides details about how Clemson became involved, as well as Extension’s role in implementing programs in local communities having diverse needs. The presentation describes development along with many other issues involved with developing and funding long term programs that meet regulatory requirements.