The Sediment and Erosion Control Research and Education Facility at North Carolina State University

R. A. McLaughlin¹, N. Rajbhandari¹, W. F. Hunt², D. E. Line², R. E. Sheffield², and N. M. White³

Abstract

Field testing of existing and new sediment and erosion control products or systems has been problematic when conducted on active construction sites. Uncertainty about runoff quantity and quality due to weather patterns and construction activities makes objective, replicated experiments very difficult. These problems will be largely overcome with the establishment of a new site for conducting tests of sediment and erosion control systems. The Sediment and Erosion Control Research and Education Facility has been established at the Lake Wheeler Road Field Laboratory in Raleigh as part of the National Training Center for Land-Based Technology and Watersheds. Initial funding is being provided by the Sediment Control Commission and the DENR Division of Water Quality under the EPA 319(h) program. This will be the first site in North Carolina and one of the few in the nation to be dedicated to the evaluation and improvement of sediment and erosion control systems. The results of these studies will be further tested under typical construction conditions around the state. The Lake Wheeler Road site will also provide a location for education and training for state and local sediment control programs. Keywords. Soil erosion, sediment control, water quality.

Introduction

For several years we have attempted to establish research sites on construction projects in order to determine the effectiveness of several sediment control measures. In most cases, the variability in natural rainfall and the constantly changing landscape conspired to make the resulting data extremely difficult to interpret. As a result, we have established an area in which we can evaluate current and proposed sediment and erosion control practices under more controlled conditions at the NCSU Lake Wheeler Road Training Center. This site is ideally located as it is convenient to campus for research and it is centrally located for training and demonstrations. It also has several irrigation ponds and a pumping network which can provide sufficient water for testing purposes. Research to quantify the effectiveness of current and experimental sediment control practices will provide a basis for future recommendations. The main focus of this effort will be in the following areas:

Inlet Protection: We will evaluate fabric, block and gravel, and sod protection practices for their ability to reduce sediment movement into the drain. They will be established in a manner to allow the source water to be diverted to any combination of the three inlets, which will facilitate replication and comparisons.

Sediment Traps and Rock Dams: Rock dams and temporary sediment traps are used in many situations where a sediment basin is not desirable. Because of the similar rock specifications in both, we will construct a rock dam without the fine gravel layer for initial evaluation under different storm event conditions. We will then add the specified fine gravel layer and conduct similar tests of sediment removal under different storm events. Further modifications will be evaluated, including establishing a shallow standing pool, using a finer gravel or filter fabric, or other approaches to increasing efficiency. In addition, modifications to the overflow design will be tested to improve stability and reduce washout.

[1] Richard A. McLaughlin, Associate Professor, Narayan Rajbhandari, Senior Researcher, Soil Science Department; ² William F. Hunt, Extension Specialist, Daniel E. Line, Extension Specialist, Ronald E. Sheffield, Extension Specialist, Biological and Agricultural Engineering Department; ³Nancy M. White, Extension Associate Professor, School of Design, North Carolina State University, Raleigh, NC. Corresponding author: Richard A. McLaughlin, Ph.D, Soil Science Department, Box 7619, NCSU, Raleigh, NC 27695-7619. Ph. 919-515-7306; Fax 919-515-7494; email rich_mclaughlin@ncsu.edu.

Sediment Fence Practices: Silt fence has been widely used for slowing runoff to allow settling before the runoff leaves a site. They appear to work well in some situations and to fail in others. We will establish silt fence along a slope (<5% perpendicular to fence) and direct runoff of a range of flows and sediment loads into the fence.

Runoff Conveyance Measures: This area will have a number of channels established in which different stabilizing systems can be installed and tested. As indicated for the basin testing, a large volume of water can be released to provide enough water to simulate a storm event. We will establish three channels of different slopes in which to evaluate fiber mats alone and in combination with seeding, grass seeding, and riprap. In addition, rock check dams will be evaluated using a variety of recommended and modified compositions.

Site Design

The site has a 300 m³ source pond which is fed from the farm irrigation pond. A 30 cm pipe exits the bottom of the pond to deliver the water into the areas for testing. A computer-controlled electric valve is used to establish flow rates and patterns. Flows of up to 0.2 m³/s can be generated with this system. At the pipe end, soil is delivered into the stream of water at a controlled rate to simulate typical runoff loading from construction sites. The resulting mix is then directed into the sediment control device, such as sediment traps, silt fences, and inlet protection systems. Automatic samplers are installed at inlet and outlet areas. A constructed wetland with a forebay is already in place to receive the water produced during testing to further polish the water before discharge.