Lower Granite Dam Breach Proposal2

1. Lower Granite Dam
Breach Proposal
Using WinDAM B Software

2. Summary
This presentation is an alternative to the US Army Corp of Engineers breaching
plan for Lower Granite Dam. This alternate breaching plan can be performed
safely and at a significantly lower cost and while remaining consistent with the
2002 EIS/ROD. The plan described fulfills most of the needs of a supplemented EIS.
o The spillway and turbines can be used to draw the reservoir down without
modification.
o The earthen embankment can be notched with minimal excavation equipment.
o Slow drawdown results in minimal damage to river banks and railroads .
o The remaining embankment can be hydraulically breached in a non-catastrophic
manner with a peak flow of 151k cfs.
o The outflow during the breach will not adversely affect dams downstream.
o The new river channel will be formed with higher spring flows.

3. WinDAM B Software
Windows Dam Analysis Modules (WinDAM) is software developed for the analysis
of earthen embankments. It was created by the US Department of Agriculture-
Agricultural Research Service, US Department of Agriculture- Natural Resources
Conservation Service, and Kansas State University. Version B, which was used in
this analysis, was released in 2011. The primary functions of WinDAM B are:
●Hydraulically route river flow through, around, and over a single earthen dam.
●Estimate spillway erosion.
●Estimate erosion of the earthen embankment caused by overtopping of the dam
embankment.

4. Lower Granite Dam Geometry
with notch location

5. Assumed Dam Fill Properties
 Dam Fill Total Unit Weight= 124 lb/ft3
 Dam Fill Erodibility= 10 (ft/hr)/lb/ft2
 Dam Fill Undrained Shear Strength 2000 lb/ft2
 Dam Fill Critical Shear strength 0.1 lb/ft2

6. Drawdown Pool Elevation
600
620
640
660
680
700
720
740
0 10 20 30 40 50 60 70 80 90 100 110
Elevatino(feet)
Time (days from start)
Spillway and 1 Turbine
Spillway Crest
4 Turbines
Begin Hydraulic Breach

7. Dam Breach Hydrograph
Flows of 50k cfs, 120k cfs, 200k cfs

8. Dam Breach Hydrograph
Close-up of first 30 hours
Maximum flow during breach= 151k cfs

9. Dam Breach Process
38 minutes into head-cut process
Dam Profile View
Pool
Head-cut initiation
Channel Width
Dam Plan View

10. Dam Breach Process
60 minutes into head-cut process

11. Dam Breach Process
90 minutes into head-cut process

12. Dam Breach Process
165 minutes into head-cut process

13. Dam Breach Process
180 minutes into head-cut process

14. Dam Breach Process
Channel Widening Process at 218 minutes
Notch completely breached
Widening begins

15. Dam Breach Process
Channel Widening Process at 547 hours
Widening complete at 750 feet

16. Head-cut/Breach Width Progression
50k cfs
120k cfs
200k cfs

17. Channel Width
 8-9 ft/sec velocities required to cause channel widening using assumed dam
fill properties
 750 foot wide channel requires 200k cfs
 1000 foot wide channel requires ~250k cfs
 1200 foot wide channel requires ~300k cfs
0
20
40
60
80
100
120
140
160
2014 and 2015 Flows at Lower Granite Dam
2014 Flow (x1000cfs) 2015 Flow (x1000cfs)