1. EROSION TECHNOLOGY for SITES Earth Spillway Integrity Analysis Phase 2: Inputs and Equations EROSION TECHNOLOGY for SITES Earth Spillway Integrity Analysis Phase 2: Inputs and Equations EROSION MEASUREMENT TRAINING: Maricopa County, AZ October 2011

2. 3 PHASE Spillway Erosion Model 1.SURFACE EROSION (Cover Destruction) 3. HEADCUT ADVANCE 2. CONCENTRATED FLOW EROSION

3. SPILLWAY EROSION PHASES 1. SURFACE EROSION 1. SURFACE EROSION (Cover Destruction) 2. CONCENTRATED FLOW EROSION (Headcut Formation) (Headcut Formation) 3. HEADCUT ADVANCE

4. PHASE 2 CONCENTRATED FLOW EROSION

5. PHASE 2 Concentrated Flow Surface Detachment.  r = k d (  e -  c )  e =  (d+  d)S Stress equation applies when eroded depth (  d) is less than approach critical flow depth (phase 2). k d = coefficient of detachment (material property)  c = critical tractive stress (material property)

6. SURFACE DETACHMENT

7. cc ee rr

10. DETACHMENT RATE COEFFICIENT The detachment rate coefficient may be externally determined and entered directly in SITES or estimated by SITES from soil properties.

12. Summary of Factors to compute Kd  Dry Density,  d  Percent finer than 2  (% clay)  Practical range is from 0.01 to 10  Number is inversely related to resistance to erosion – low value is high resistance, high value is low resistance  Note units are in ft/hr of downward erosion per unit applied stress of lb/ft 2

13.  Jet Erosion Test (JET)

15. Jet Erosion Test in NY Spillway

16. CRITICAL STRESS for Detachment Critical stress based on loose particle condition for all materials.

17. Parameters Impacting Phase 2 Erosion

18. SPILLWAY EROSION PHASES 1. SURFACE EROSION 1. SURFACE EROSION (Cover Destruction) 2. CONCENTRATED FLOW EROSION 3. HEADCUT ADVANCE