SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008

1. PART 2 – SITES EARTH SPILLWAY EVALUATION B. Earth Spillway Integrity Analysisb. Characterization of geologic materials: i & ii. History and weakness of Kh & kd SPECIALTY WORKSHOP: SITES TRAINING AND INTRODUCTION TO WINDAM ASDSO Dam Safety 2008

2. OBJECTIVES • History of Kh • Field Observations • Origin of Concepts • Kh • Kh Issues

3. 1983 -The ESFSTG was formed 1991 - ARS & SCS established DAES Team

8. History of Concepts • TR 71 The NRCS first used the Rock Material Field Classification (RMFC) system to classify rock performance for several engineering applications. • TR-71 Second Edition revised version of the RMFC system by John Moore. • Revised version of RFMC published in ASTM STP – 984 (Moore) • NEH Part 628 Chapter 52 Field Procedures Guide for the Headcut Erodibility INDEX • 2002 Chapter 12 Rock Material Classification System

9. History of Concepts • TR 71 The NRCS first used the Rock Material Field Classification (RMFC) system to classify rock performance for several engineering applications. • TR-71 Second Edition revised version of the RMFC system by John Moore. • Revised version of RFMC published in ASTM STP – 984 (Moore) • NEH Part 628 Chapter 52 Field Procedures Guide for the Headcut Erodibility INDEX • 2002 Chapter 12 Rock Material Classification System

10. History of Concepts • ASAE Transactions Vol 32, No 6 “Mechanics of an Earth Spillway Failure” (Temple). • ASAE Applied Engineering in Agriculture; Vol 8, No. 2 “Estimating Flood Damage to Vegetated Deep Soil Spillways.” (Temple) • Bulletin of AEG Vol 31 No. 2, “Headcut Advance Threshold in Earth Spillways” (Moore et. al.) • 1997 ASAE Transactions Vol. 40, No 3 “Headcut Advance for Earth Spillways” (Temple and Moore)

11. History of Concepts • ASAE Transactions Vol 32, No 6 “Mechanics of an Earth Spillway Failure” (Temple). • ASAE Applied Engineering in Agriculture; Vol 8, No. 2 “Estimating Flood Damage to Vegetated Deep Soil Spillways.” (Temple) • Bulletin of AEG Vol 31 No. 2, “Headcut Advance Threshold in Earth Spillways” (Moore et. al.) • 1997 ASAE Transactions Vol. 40, No 3 “Headcut Advance for Earth Spillways” (Temple and Moore)

12. HEADCUT MIGRATION dx/dt = C (A - Ao) dX/dt = rate of headcut migration, C = material-dependent advance rate coefficient, A = hydraulic attack, and Ao = material-dependent threshold.

13. HYDRAULIC ATTACK A = (q q H

14. MATERIAL-DEPENDENT PARAMETERS AO & C are a function of Kh = headcut erodibility index

15. [ _ 189 Kh1/2exp(-3.23/ln(101Kh)) ]1/3 Kh> 0.01 AO = 0 Kh< 0.01 AND - 0.79 ln(Kh) + 3.04 Kh< 18.2 C = 0.75 Kh > 18.2 _

17. Kh issues • Empirical relations based on small amount of data. • Not the only parameter important to spillway erosion. • Spillway erosion is a three phase process • Erosion is dependent on spillway slope, vegetation, material detachment erodibility, flow stress, process, etc. • Large reductions in Kh may not result in spillway breach if other factors are controlling the process. • Kh is represented in logrithmic space.

18. Kh issues (continued) • Technology is relatively young and will continue to require additional research and change. • classification system is based on weighted parameters. Relative importance of each element is not completely understood. • The classification system includes materials from soils to massive rock but • Difficult to determine soil structure • Original development of Kh for soil did not include soil structure. Elements were commonly assumed equal to 1 with the exception of material strength (Ms)