Selected Site BMPs: Why s the Water Muddy? John C. Hayes, Ph.D., P. E. Biosystems Engineering Clemson University
The BMP worked fine until last week when it rained!
Turbidity
Best Management Practices or
Better Management Practices or
Boondoggle Management Practices???
WHAT IS A BMP? Structural or Non- Structural Measure that controls runoff, erosion, or sediment
EXAMPLES OF STRUCTURAL BMPs Sediment Ponds Silt or Filter Fence Sediment Traps Rock Ditch Checks Vegetative Filter Strips Stormwater Detention Infiltration Zones Etc., etc.
EXAMPLES OF NON- STRUCTURAL BMPs Riparian Zones Buffer Strips Phasing/Staging Vegetative Covers Topsoiling Etc., etc.
Geologic Erosion
Accelerated Erosion
EROSION VS SEDIMENT CONTROL EROSION CONTROL Keeps soil from leaving soil matrix SEDIMENT CONTROL Removes sediment from flowing water
TYPES OF EROSION
Raindrop
Rill
Channel /Gully
PREDICTING EROSION USLE/RUSLE A = R K LS C P Some things we can control Some things we cannot control
Rainfall We cannot control R factor Florence: R = ~250 Clemson: R = ~300 NOT evenly distributed through the year
Soil Erodibility We have little control on K factor Silt loam: K = 0.32 Sandy loam: K = 0.24 Loamy fine sand: K = 0.17
Length-Slope We have limited control on LS factor 9% slope, 72.6 ft: LS = 1.0 10 % slope, 200 ft: LS = 2.4 15 % slope, 200 ft: LS = 4.3 20% slope, 200 ft: LS = 11.3
Cover Management Undisturbed Forest: C =.001 to.0001
Cover Management 0.5 tons/ac straw C = 0.3 2.0 tons/ac straw C=0.09 4.0 tons/ac woodchips C=0.42
Practice Factor 0.3<P<1.0
USLE/RUSLE A = R K LS C P
EXAMPLE 1 Typical => R = 250 Sandy loam soil => K = 0.24 Slope Length = 300 ft Slope = 5% } Mature Forest => C = 0.001 Practice Factor => P = 1 => LS = 1.0 A = 0.06 tons/ac-yr
EXAMPLE 2 Typical => R = 250 Sandy loam => K = 0.24 Slope Length = 300 ft } => LS = 1.0 Slope = 5% Bare Soil (bulldozed) => C = 1 Practice Factor => P = 1 A = 60 tons/ac-yr
Is this obvious? A = 60 tons/ac-yr This is equivalent to about 0.4 in. of depth!
EROSION REDUCTION Phasing Scheduling Vegetation, Fabrics and Mulches
WHAT CAN WE DO ABOUT IT? or Local Problems and Solutions
Storm Water Runoff BMPs Pipe slope drain Runoff diversion measures Temporary stream crossing Construction de-watering 31
Pipe Slope Drain Description: Pipe slope drains are used when it is necessary for water to flow down slope without causing erosion, especially before slope has been stabilized or before permanent drainage structures are installed. Pipe slope drains can be temporary or permanent depending on installation and material used. 32
33 Pipe Slope Drain
Pipe Slope Drain Troubleshooting: 34
Runoff Diversion Measures Description 35 Diversion dikes and berms (ridges of compacted soil) are used to divert upslope clean water runoff from crossing areas where there is high risk of erosion. Temporary silt ditches or swales (excavated depressions) are used to prevent sediment laden runoff from leaving site before being treated by sediment control BMP.
Runoff Diversion Measures Silt Ditches 36
Temporary Stream Crossing Description: A temporary stream crossing is typically a bridge or culvert erected to provide safe and stable way for construction vehicle traffic to cross a running watercourse. Typically only used for DOT projects because they require extra permitting (DHEC and/or Corps of Engineers) 37
Construction De-watering Description: 38 Construction de-watering involves removing storm water or ground water from bore pits, trenches and other excavations. Usually this removal of water involves pumping of water to appropriate receiving area such as a sediment basin, sediment trap, or geotextile filter bag.
Erosion Prevention BMPs Surface Roughening Temporary Stabilization Mulching Erosion Control Blankets (ECBs) Turf Reinforcement Mats (TRMs) 39
Erosion Prevention BMPs Final Stabilization Outlet Protection Dust Control Polyacrylamide (PAM) 40
Surface Roughening Description: Creation of horizontal depressions, steps or grooves that run parallel to contour of land. Methods include: 41 Tracking Stair-step grading Grooving
Surface Roughening Tracking (Correct Installation) 42
Surface Roughening Tracking (Incorrect Installation) 43
Temporary Stabilization Description: Reduce erosion and sedimentation by stabilizing disturbed areas that would otherwise lay bare for long periods of time before they are worked or stabilized. Any disturbed areas that will not be worked for 14 days or more must have temporary cover 44 applied by 14th day (DOT has 7 day requirement).
45 Temporary Stabilization
Mulching Description: 46 Temporary practice where materials such as grass, hay, wood chips, straw, or compost are placed on exposed or recently planted soil surfaces. Natural woody vegetative material cleared from site can be ground to create usable wood chips that are spread back onto disturbed areas.
Mulching Blowing Straw Adding Tackifier 47 Wood Mulch
Mulching Pneumatic Application of Wood Mulch 48
Erosion Control Blankets Description: Erosion Control Blankets (ECBs) are temporary erosion control BMPs that hold seed and soil in place, degrading over time period of approximately 1- to 3-years as vegetation becomes established. 49
Turf Reinforcement Mats Description: Turf Reinforcement Mats (TRMs) are permanent erosion control BMPs often used in areas of concentrated flows. Composed of synthetic materials, TRMs provide immediate erosion protection and outstanding long-term 50 erosion resistance.
51 ECBs / TRMs
52 ECBs / TRMs
ECBs / TRMs Troubleshooting: 53
Final Stabilization Description: Several methods can be used for final stabilization: Permanent seeding and planting of grasses Permanent planting of ground cover plants Sodding 54
Final Stabilization Final stabilization means that all soil disturbing activities at the site have been completed and either of the two following criteria are met: 1. An uniform perennial vegetative cover with a density of 70% of native background vegetative cover has been established on all unpaved areas and areas not covered by permanent structures; or 2. Equivalent permanent stabilization measures (riprap, gabions, or geotextiles) have been employed. 55
The Same Coverage? OK OK 70% 70% 56
57 Final Stabilization
Outlet Protection Description: 58 Protects immediate area around pipe and culvert outlets from scour and deterioration by dissipating flow energy. Outlet protection includes TRMs, riprap, grouted riprap, concrete, gabion baskets, or other structural measures.
Outlet Protection 59 TRM Outlet Protection Riprap Outlet Protection
Dust Control Description: 60 Practices that help reduce surface and air movement of dust from disturbed soil surfaces. Dust control methods include: project phasing, vegetative cover, mulch, sprinkling water, spray-on adhesives, barriers and covers.
61 Dust Control
Polyacrylamide (PAM) Description: Anionic polyacrylamides (PAM, or polymers) are used as a non-toxic chemical temporary tackifier for controlling soil erosion and as a flocculant to aid sedimentation. Polymers are available as: Dry/Powder Polyacrylamides Liquid Polyacrylamides Solid/Block Polyacrylamides 62
63 Polyacrylamide (PAM)
Sediment Control BMPs Sediment basin Multi-purpose basin Sediment dam (trap) Silt fence Rock ditch check Sediment tube ditch check 64
Sediment Control BMPs Stabilized construction entrance Filter fabric inlet protection Block and gravel inlet protection Hardware fabric and stone inlet protection Pre-fabricated inlet protection 65
Sediment Basin Description: A structure designed to capture sediment from storm water runoff before it leaves construction site. Basins should be constructed before any grading takes place within drainage area. 66
67 Sediment Basin
Troubleshooting: Sediment Basin 68
Multipurpose Basin Description: Permanent detention basins designed for use as temporary sediment basins during construction phase of project. 69 During Construction After Construction
Sediment Dam (Trap) Description: Formed by excavating pond or by placing earthen embankment across low area or drainage swale. An outlet or spillway is constructed using No. 5 washed stone and Class B riprap aggregate. 70
71 Sediment Dam (Trap)
Sediment Dam (Trap) Troubleshooting: 72
Silt Fence Description: 73 Used as temporary perimeter controls around sites where there will be soil disturbance due to construction activities. Consist of posts with geotextile fabric stretched across posts (nonreinforced) preferably with wire support fence (reinforced).
Silt Fence 74 Silt Fence with Tie-backs
75 Silt Fence
Troubleshooting: Silt Fence 76
Troubleshooting: Silt Fence 77
Troubleshooting: Silt Fence 78
Troubleshooting: Silt Fence 79
Rock Ditch Check Description: 80 A rock ditch check is a small, temporary or permanent rock fill dam constructed across drainage ditch, swale, or channel to lower speed of concentrated flows. Rock must be placed by hand or mechanical placement (no dumping of rock to form dam) to ensure that center of check is lower than edges.
81 Rock Ditch Check
Sediment Tube Ditch Check Description: 82 Sediment tubes are elongated tubes of compacted geotextiles, curled excelsior wood, natural coconut fiber or hardwood mulch. Sediment tubes may be installed in drainage conveyance swales as ditch checks to help reduce effects soil erosion and retain sediment.
83 Sediment Tube Ditch Check
Stabilized Construction Entrance Description: 84 A stabilized construction entrance is temporary stonestabilized pad located at points of vehicular ingress and egress on construction site to reduce amount of mud, dirt, and rocks transported onto public roads by motor vehicles equipment and runoff.
Stabilized Construction Entrance 85
Filter Fabric Inlet Protection Description: Filter fabric is used for inlet protection for small storm water flows (0.5 cfs or less) with low velocities and where inlet drains relatively flat area (slopes no greater than 5%). This practice should not be used where inlets are paved or where inlets receive concentrated flows such as in streets or highway medians. 86
87 Filter Fabric Inlet Protection
Filter Fabric Inlet Protection Troubleshooting: 88
Filter Fabric Inlet Protection Troubleshooting: 89
Block and Gravel Inlet Protection Description: Block and gravel filters can be used where heavy flows and higher velocities are expected and where overflow capacity is necessary to prevent excessive ponding around structure. 90
Block and Gravel Inlet Protection 91
Block and Gravel Inlet Protection 92
Hardware Fabric and Stone Inlet Protection Description: 93 Supported wire material with filter stone can be used where concentrated flows may be expected. Wire mesh and gravel protection is used when flows exceed 0.5 cfs and when construction traffic will occur over inlet.
Pre-Fabricated Inlet Protection Description: Structures designed to keep silt, sediment and construction debris from entering pipe systems through open inlet structures. 94
Pre-Fabricated Inlet Protection Installation: Weighted Sediment Tubes -Install lying flat on ground. 95
Pre-Fabricated Inlet Protection Installation: Rigid Inlet Filters - Installed to ensure BMP completely encloses inlet. 96