Potential Pollutants Sediment Chemical N, P, Pesticides, Oil & Grease Concrete Washout Biological Sanitary Waste Solid Waste Construction Debris

Erosion Starts with the Soil! ≥100 years to form 1 inch of topsoil

Mass grading = High Erosion Potential

Construction “Soil” Realities MOST topsoil has been removed Little to no organic matter present Mostly mineral (sand, silt, clay) left behind Compacted (nowhere for water to infiltrate) Easily Erodible and A LOT of runoff

Low Impact Development or LID is an ecologically friendly approach to land development and storm water management. The goal of LID is to mitigate development’s impacts on the land, water and air. Low impact development infiltrates more rain and sheds less runoff, to protect water quality and reduce flood peeks. Bal ouchek et al, UW-Madison

The Erosion Process

Exposed Soil

TAXPAYER EXPENSES Cleaning out sediment plugged storm sewer intakes, pipes, structures, basins…

Types of Erosion Sheet & Rill Erosion Gully Erosion Soil erosion is a three-step process involving the detachment, transport and deposition of soil particles. Wind Erosion: Wind is the transport mechanism moving a thin layer of soil from land to a point of deposition Stream Bank Erosion: scouring away of stream banks; repeated high flows of extended duration is the cause Sheet & Rill Erosion: uniform movement of a thin layer of soil from sloping, bare, unprotected land. Falling raindrops detach soil particles which go into solution as runoff occurs. Rills form with longer, harder rains when runoff volumes accelerate Gully Erosion: rill erosion evolves into gully erosion as runoff increases, from one heavy rain or a series of rains over time. A gully is a scoured out area that is not crossable with tillage or grading equipment. Stream Bank Erosion Wind Erosion

Sheet and Rill Erosion

Gully Erosion

Wind Erosion

Factors Influencing Erosion Coverage Soil Rainfall Slope Practice

RUSLE2 - Revised Universal Soil Loss Equation C x K x R x LS x P = A FIVE FACTORS INFLUENCING EROSION C Coverage K Erodibility R Rainfall (only one that can’t be controlled!) LS Length of Slope P Conservation Practice A Annual soil loss tons per acre / per year, estimated

K - Soil Particle Sand (0.05-2.00 mm) Silt (0.002-0.05 mm) Clay (<0.002 mm)

K - Soil Texture % Sand % Silt % Clay

K - Soil Structure Single-Grained: usually sands Granular: resembles crumbs, usually surface soils where roots grow Platy: thin flat plates of soil, usually found in compacted soil-natural or not Angular: Irregular blocks, usually found below surface soils, higher clay content http://soil.gsfc.nasa.gov/pvg/prop1.htm

Hydrologic Soil Groups

Soil Organic Matter Content Clay (assumes 2% OM content) K – Soil Most Likely to Erode… C x K x Rx LS x P = A Soil Organic Matter Content Sandy Loam Loam Clay (assumes 2% OM content) OM <.05% .27 .38 OM 2% .24 .34 .20 - .13 OM 4% .19 .29 One variable to erosion is soil organic matter content – less OM = more erosion.

C x K x R x LS x P = A Surface Coverage (Mulch) C Factor Bare Ground 1.0 1 Ton Straw Mulch Per Acre 0.13 2 Ton Straw Mulch Per Acre 0.02 98% reduction in erosion!!!!

C x K x R x LS x P = A Slope Reduction Length LS Factor 30% 75 feet 4.44 25 feet 1.86 10% 0.57 30% Slope v. Length - 58% reduction in erosion. 30% v. 10% Slope @ 25 Feet – 87% reduction in erosion

A Note About Slopes can be expressed three different ways! Inch drop per foot % Slope X:1 12” 100% 1:1 6” 50% 2:1 4” 33% 3:1 3” 25% 4:1 2.4” 20% 5:1 2” 16.7% 6:1 1.7” 14.3% 7:1 1.5” 12.5% 8:1 1.3” 11.1% 9:1 1” 8.3% 10:1

C x K x Rx LS x P = A Conservation Practice 38% reduction in erosion!! Surface Roughening P Factor Compact & Smooth 1.3 Loose & Rough, 12” Deep 0.08 38% reduction in erosion!!

Class Exercise Soil texture Clay Soils Ribbon Test