SEDIMENT & EROSION CONTROL ON CONSTRUCTION SITES FIELD GUIDE Cooperative Extension Service University of the Virgin Islands #2 John Brewers Bay St. Thomas, USVI 00802-9990 (340) 693-1082 http://rps.uvi.edu/CES/wqindex.html Division of Environmental Protection V.I. Department of Planning & Natural Resources 45 Mars Hill Frederiksted, USVI 00841 (340) 773-1082 http://www.dpnr.gov.vi/ This Sediment & Erosion Control on Construction Sites Field Guide is published by the University of the Virgin Islands Cooperative Extension Service, Kwame Garcia, State Director. No endorsement of products or Published by the University of the Virgin Islands Cooperative Extension Service firms is intended, nor is criticism implied of those not mentioned. Issued by the Virgin Islands Cooperative Extension Service and the U.S. Department of Agriculture in furtherance of the acts of May 8 and June 30, Funded by a federal Clean Water Act grant from the Virgin Islands Department of Planning 1914. Extension programs and policies are consistent with federal and state laws and regulations on and Natural Resources §319(h) Nonpoint Source Pollution Management Program. nondiscrimination regarding race, color, national origin, religion, gender, age, disability or gender preference. SEDIMENT & EROSION Best Management Practices to Control Sediment & Erosion on Construction Sites SEDIMENT AND EROSION CONTROL ON CONTROL ON CONSTRUCTION CONSTRUCTION SITES FIELD GUIDE SITES FIELD GUIDE INTRODUCTION.............................................. 1 BEFORE EARTH CHANGE....................................... 2 Preserve and Protect Natural Vegetation ............................... 3 Perimeter Dikes and Swales........................................ 5 Silt Fencing................................................... 6 DURING EARTH CHANGE....................................... 8 Land Grading ................................................. 8 Stabilized Construction Entrance ................................... 10 Soil Sealers / Binders ........................................... 11 Dirt Road Drainage ............................................ 12 Soil Retaining Walls............................................ 14 Temporary Seeding ............................................ 16 Mulches, Mats and Geotextiles..................................... 18 Filter Strips.................................................. 20 Drainage Swales............................................... 22 Temporary Storm Drain Diversion .................................. 24 Check Dams ................................................. 25 Sediment Trap................................................ 26 Temporary Sediment Basin ....................................... 29 Storm Drain Inlet Protection ...................................... 30 Outlet Protection.............................................. 31 Gabion Inflow Protection ........................................ 33 AFTER EARTH CHANGE ....................................... 34 Permanent Seeding and Planting.................................... 34 Porous Paving ................................................ 36 Rain Gardens ................................................ 38 REFERENCES................................................ 39 Published by the University of the Virgin Islands Cooperative Extension Service Funded by a federal Clean Water Act grant from the Virgin Islands Department of Planning and Natural Resources §319(h) Nonpoint Source Pollution Management Program. i Best Management Practices to Control Sediment & Erosion on Construction Sites Best Management Practices to Control Sediment & Erosion on Construction Sites INTRODUCTION BEFORE EARTH CHANGE Sediment eroded from dirt roads, construction sites and other cleared areas is the number Planning before clearing and construction is important to conserve valuable topsoil, prevent one pollutant harming water quality in the Virgin Islands (DPNR-DEP & USDA-NRCS, costly landslide and flooding problems, conserve natural areas and native species, reduce 1998). A 1986 study of erosion rates on St. Thomas and St. Croix estimated erosion from paved areas (impervious cover), prevent property damage and minimize stormwater runoff dirt roads to be 591 tons/acre/year (Wernicke, Seymour & Mangold, 1986). Studies of ero- and downstream pollution. The first step in this planning process is to identify the physical sion rates in St. John’s Fish Bay watershed found soil loss from dirt roads to be between 100 characteristics of the property: soils, topography (slopes, rock outcrops, etc.), hydrology to 600 tons per year (MacDonald, et al., 1997; Sampson, 1997). Therefore, controlling ero- (guts, ponds, water flow paths), and vegetation (endangered species, large trees). sion and soil loss on construction sites, dirt roads and other cleared areas is key to protecting V.I. coastal waters. Knowing soil properties on site prior to construction (or even purchase) is important to select the best site for intended use and prevent costly mistakes. The USDA Natural There is a big difference between practices that prevent or reduce erosion and those that Resources Conservation Service, through it’s Soil Survey of the U.S. Virgin Islands, has rated remove soil (or sediment) from stormwater. Erosion control practices hold soil in place and soils for limitations for different uses such as septic systems, construction fill, road beds, and reduce soil removal by storm water. The most effective way to control erosion is to building foundations. Common soil limitations found in the Virgin Islands include high preserve existing vegetation and replant cleared or bare areas as soon as shrink-swell clays, high soil erodibility, very steep slopes, shallow or stony soils, and possible. excessively dry climate. Sediment control practices remove eroded soil from runoff before it leaves the property. Knowing the site’s topography is important so that the building designer and contractor can These practices are NOT as effective as erosion control because they do not remove most work with the natural contour of the land to reduce erosion, minimize excavation, reduce clay particles, and most of the soils in the Virgin Islands are clay. For example, clay particles flooding and minimize costs. The topographic site features that should be mapped for the site pass through silt fence material and take a very long time to settle out of runoff in holding include slope, rock outcrops, water features and floodplains. ponds. It is much easier and more cost-effective to keep the soil in place than it is to attempt to remove soil from stormwater. The hydrology of a site is very important to minimize flooding, erosion and property damage both on and off site. The information that is important to know includes the water pathways An effective sediment and erosion control plan should: across the property, whether or not guts or wetlands are present on the property, the depth C Minimize clearing: use site fingerprinting, buffers/setbacks, construction phasing. to the groundwater, the distance to nearby surface waters (guts, ponds, wetlands, coastal waters) C Prevent off-site runoff from flowing across bare soils: use perimeter dikes/ and whether or not the property is in a floodplain. swales, diversions. C Stabilize bare soils on the site: use erosion control mats, planting, retaining walls. It is also important to scout the vegetation on the property to observe the existing C Remove sediment from runoff before it leaves the site: use stabilized construc- vegetation types (to know what kinds of vegetation are native and also what can be planted tion entrances/exits, silt fences, sediment traps, check dams. after construction), and to determine if and where there are endangered species, critical C Plan soil disturbance activities for the dry season. habitats, and large trees located on the site. This field guide provides a brief description of and installation information for sediment and Preserving existing vegetation and re-planting cleared/bare soils as soon as erosion control practices that should be installed during all phases of construction: before possible after earth change is the most effective way to control erosion. Plant land clearing (or earth change), during land clearing and construction, and after construc- cover reduces erosion potential by: tion. Some practices can be used in more than one phase of construction, and so are intro- duced at the first instance where they can be used. Sediment & erosion control practice • Protecting the soil surface from the impact of falling rain drops (reducing erosion); selection for construction sites should be based on the type of construction activity and the • Slowing runoff velocity (or speed) and allowing sediment to settle out (reducing off-site site conditions (soils, slope, vegetation). More detailed practice design and installation infor- sediment loss); mation can be found in the 2002 V.I. Environmental Protection Handbook (Wright, • Physically holding the soil in place with plant roots (erosion control); and 2002). • Increasing infiltration (or seepage) rates by improving the soil’s structure and porosity. 1 2 Best Management Practices to Control Sediment & Erosion on Construction Sites Best Management Practices to Control Sediment & Erosion on Construction Sites Preserve & Protect Natural Vegetation Vegetation preservation and protection minimizes the amount of disturbed soil exposed to the erosive forces of wind and rain, and provides natural buffers to slow runoff and filter