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

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

3. Mass grading = High Erosion Potential

4. 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

5. 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

6. The Erosion Process

7. Exposed Soil

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

10. 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

11. Sheet and Rill Erosion

12. Gully Erosion

13. Wind Erosion

14. Factors Influencing Erosion
Coverage
Soil
Rainfall
Slope
Practice

15. 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

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

17. K - Soil Texture
% Sand
% Silt
% Clay

18. 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

19. Hydrologic Soil Groups

21. 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
OM 4%
.19
.29
One variable to erosion is soil organic matter content – less OM = more erosion.

22. 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!!!!

23. 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% 25 Feet – 87% reduction in erosion

24. 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

25. 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!!

27. Class Exercise
Soil texture
Clay Soils
Ribbon Test