Module 2: Erosion Fundamentals

n Identify different types of water erosion n Identify different types of water pollution n Understand soil susceptibility to erosion n Identify erosion control approaches Learning Objectives

Construction, Erosion, and Sediment n Construction increases runoff volume and sediment load n Can result in flooding and degradation of water quality in receiving waters n Degradation includes sediment loads and chemicals bound to soil particles n Can be harmful to fish, wildlife, livestock, vegetation, and humans

Pollution Prevention Approach n Stormwater management system approach n Best Management Practice tools

Types of Water Erosion n Splash Erosion n Sheet Erosion n Rill and Gully Erosion n Streambank Erosion n Shoreline Erosion n Snowmelt Erosion

Splash Erosion n Caused by raindrop impact n Soil particles detached n Soil/water solution created n Soil structure degraded n Crust can form after drying

Sheet Erosion n Uniform sheet flow of water over surface n Causes pedestalling of plants n Uniform removal of soil n Typically occurs on low-gradient slopes

Rill and Gully Erosion n Concentrated flow n Caused by topographic variation n Higher runoff velocities n Channels deepen over time, progress uphill n Can move large amounts of sediment

Streambank Erosion n Naturally occurring process n Can be accentuated by upstream construction activity n Bank sloughing can be triggered by erosion of the streambank toe n Deep, binding rootmass required for stability

Shoreline Erosion n Lakeshores and ocean coastlines n Caused by high-energy wave action n Can cause bank sloughing n Stabilizing rootmass or rock required

Snowmelt Erosion n Soil freezing can detach particles n Snow accumulation in or above construction area n Frozen ground retards infiltration n Rapid warming is a problem

Erosion Prediction using the Universal Soil Loss Equation A=RKLSCP n A = Average Annual Soil Loss n R = Rainfall Amount n K = Soil Erodibility n L = Slope Length n S = Slope steepness n C = Cover Factor n P = Conservation Practices

Rainfall Factor (R) n Rainfall intensity and duration n Built in database for rainfall intensity n As rainfall intensity increases, erosion increases n As rainfall duration increases, erosion increases

Soil Erodibility Factor (K) n Relates to soil texture and rock content n Silty soils are typically most erodible n Sandy soils have better infiltration, larger particles n Clay soil have better cohesion

Slope Factors n L = Length of Flow Path n Longer flow paths have more erosive power n S = Slope steepness n Steep slopes have higher runoff velocities

Cover Management Factor (C) n Erosion rate directly proportional to the amount of vegetation cover protecting the soil surface n Vegetation reduces rainfall impact energy n Vegetation promotes infiltration n Vegetation reduces runoff velocity n Vegetation traps sediment n Very important erosion control factor

Conservation Practices Factor (P) n Human manipulation of the soil surface to discourage erosion n Provides slope storage n Surface roughening n Pitting n Implemented on the contour

Example 1, Consider a 1 acre area n In an area that receives 0.3 m (12 in) of annual precipitation, 1,234 m 3 (1 acre-ft) of water is applied to the soil surface n 1,234 m 3 (1 acre-ft) = 1,234 m 3 (325,000 gal) n m (1 in) rainstorm = 102 m 3 (27,000 gal) water n 102 m 3 (27,000 gal) water = 101,604 kg (112 tons) n 51 kg (112 lbs) 500 mg/l TSS

Example 2, consider 1 acre of bare soil n Apply m (1 in) of rain over a 1-hour period n Sandy loam texture  90% infiltration, 11.4 m 3 (3,000 gal) runoff n Silt loam texture  40% infiltration, 60 m 3 (16,000 gal) runoff n Clay loam texture  20% infiltration, 83 m 3 (22,000 gal) runoff

Impacts of Erosion and Sedimentation n Economic losses n Environmental Impacts n Roadway Impacts

Economic Impacts of Erosion n Direct Costs  Highway repair costs  Maintenance costs n Indirect Costs  Losses in soil productivity  Flooding

Environmental Impacts of Erosion n Fisheries n Water Quality Impairment n Air Quality Impairment from dust n Loss of topsoil n Weed encroachment on bare ground

Roadway Impacts of Erosion n Culvert plugging n Drainage ditch filling n Road base saturation n Water flow onto roadway n Weed encroachment n Increased maintenance

Types of Wind Erosion Wind Erosion can transport sediment by suspension, saltation or surface creep.

Suspended Particle Movement n Light weight particles n Transported at high altitudes n Transported long distances n Dust often visible

Particle Saltation n Saltation is the bouncing of particles across the soil surface n Particle impacts may dislodge additional particles n Particles move horizontally n Moderate to strong winds n May damage vegetation

Particle Creep n Heavy Particles n Rolled along soil surface n High wind conditions

Types of Water Pollutants n Sediments n Nutrients n Bulk Organics n Halogenated Hydrocarbons n Metals

Water Pollution by Sediments n Degrade aquatic habitats n Clog drains, culverts, sediment catchments n Increase flooding severity n Impair recreational and industrial water uses

Water Pollution by Nutrients n Nitrogen n Phosphorous n Algal blooms n Depletion of oxygen in water n Source = sewer lines n Source = fertilized areas

Water Pollution by Bulk Organics n Oil and grease n Fuels, solvents, and lubricants n Can be toxic to aquatic organisms n May require subsequent cleanup n Spills costly, time consuming

Water Pollution by Halogenated Hydrocarbons n Resistant to decay n Chlorinated hydrocarbons n Hazardous waste n Extremely expensive and complex remediation

Water Pollution by Metals n Mine waste n Common in western Montana n Tailings, waste rock, slag n Often devoid of vegetation n Yellow and red color common n Small amounts can cause water quality violation

Approaches for Reducing Erosion n Surface Stabilization n Sediment Control n Revegetation

Surface Stabilization n Protection of soil surface n Prevention of erosion on-slope n Use of BMPs

Sediment Control n Capture of soil particles n Prevent or minimize transport n Use of BMPs

Revegetation n Minimize the extent of vegetation disturbance n Salvage of topsoil during construction n Direct haul of topsoil n Minimize compaction of replaced topsoil n Minimize the spread of weeds n Use BMPs to stabilize soil n Reseed

Review of Erosion and Vegetation Fundamentals n Road construction may increase erosion n Wind and water erosion common n BMPs should be used n BMPs for surface stabilization n BMPs for sediment control n Revegetation ultimate goal

Testing your knowledge n The next 4 slides test your knowledge of erosion, sediment control, and Montana’s climate. n The answers will be provided

Question 1 n How much rain falls in Butte during a 100-year, 24 hour storm event?

Answer n How much rain falls in Butte during a 100-year, 24 hour storm event? Answer=3.0 Inches

Question 2 n Which of the following are sediment control BMPs? A)Silt Fence B)Strawbale Barrier C)Check Dam D)All of the above

Answer n Which of the following are sediment control BMPs? A)Silt Fence B)Strawbale Barrier C)Check Dam D)All of the above

Question 3 n The base of a straw bale barrier BMP should be buried into the soil. A)True B)False

Answer n The base of a straw bale barrier BMP should be buried into the soil. A)True B)False

Question 4 n Which of the following soils are likely to be most erosive? A)Silt loam B)Clay loam C)Sandy loam D)Sand

Answer n Which of the following soil is likely to be most erosive? A)Silt loam B)Clay loam C)Sandy loam D)Sand

Take a Break n We will continue with BMP training in 15 minutes.