6. Current Efforts Underway

National Dam Safety Program has been enforced for every kind of ownership of dams in California. Dam safety issue is still actively activating for all stakeholders and interests. The table below provided by ASDSO (2005) shows how the National Dam Safety Program has improved dam safety in California.

In order to long-term dam safety assurance, various efforts are being taken. Especially, in California, seismic hazard is never eliminated. A DSOD report (Babbitt) in 1993 has revealed that at least 94 dams have been improved for seismic stability. And that effort is currently going on. The main leading organization is DSOD and USACE.

To make sure safer dam design, construction, and operation, current efforts should be sustainable, coherent, and technically improved.

Here in this section, current efforts underway of US Army Corps of Engineers are briefly introduced using some progressive cases. Material and photos are courtesy of USACE.

6.1 Dam Safety Assurance Program

Recently, seismic reevaluations are widely reviewed not only for embankment or concrete Dam, but also for appurtenant structures. Also, hydrologic capacity and spillway adequacy issues are very core of most of dam engineers worldwide. In addition to these, other dam safety relating program such as seepage is going on now.

Corps began the screening portfolio risk assessment in 2005. “Risk” is (probability of failure) x (consequence of failure). USBR has been doing this for > 10 years. Approximately 10% was screened in 2005, 2006, 2007 (30% of total inventory of 604 dams). Each of them was classified in “Dam Safety Action Classes (DSAC)”. The purpose is to fund the higher risk projects in terms of “fix the worst first”.

Current and future Investigations

6.2 Isabella Dam Case

The Main Dam is 185 ft high, zoned earth fill (nearly homogeneous) dam with foundation primarily composed of granitic bedrock except downstream area of recent thin alluvium. It has 6.5 feet freeboard over spillway design flood and 28.0 feet freeboard over gross (full) pool.

The Auxiliary Dam is 100 ft high and has homogeneous silty sand (very dense), 120 ft of alluvial soil foundation.

Courtesy of Ron Rose, USACE

Recent research illustrates some major deficiencies of Isabella dam as below.

Hydrologic deficiency
- Spillway capable of “safely” passing 33% of PMF
- PMF = 542,000 cfs, historic max = 120,000 cfs

Seismic deficiency
- Began reevaluation in 2003
- Study began in earnest in 2005
- Has accelerated greatly due to screening level
- risk assessment: Previously unrecognized seismic sources, Poor foundation (aux dam), Conduit/Tower PFM, Kern Canyon Fault, Newly found faults

Seepage
Auxiliary Dam
- Thick, permeable foundation, Homogeneous dam, but No effective seepage control
- History of seepage, Conduit in alluvium
- Seepage collars, vertical cut, no filter material
- Newly aware that the seepage was potentially a much more serious problem, immediately began an in-house seepage study

Isabella – current and future tasks
- Fault characterization; LiDAR, Trenching, Update seismic hazard analysis
- Dam & Foundation characterizations; Drilling, In-situ density testing, Deformation modeling
- Risk Analysis

Auxiliary dam
- Major remediation for seepage and seismic

Main dam
- Major remediation for seismic (also seepage)
- Remove recent alluvium and Needs to incorporate modern seepage control features

Hydrologic deficiency
– Major remediation needs to safely pass (with freeboard) 100% of PMF “do no harm”
– don’t increase frequency of downstream flooding

6.3 Martis Creek Dam

Its purpose is flood Control and future water supply. This dam was constructed in 1972.
- Elevation, top of dam 5858.0 ft.
- Gross Pool (spillway elev.) 5838.0 ft.
- Freeboard above spillway design flood pool 5.1 ft.
- Maximum height 113 ft.
- Storage capacity: Gross pool 20,400 ac. ft., Spillway design flood pool 34,600 ac. ft.

(Courtesy of Ron Rose, USACE)

Identified potential deficiencies

Hydrologic: Seepage, Overtopping potential
- Liquefaction of dam foundation (upstream and downstream) when earthquake occurs.
- Long history of test fills and associated seepage problems (1973, 1974, 1978, 1980, 1986, 1995
- 1995 test fill was pool of record: approx. 5833 (gross – 5 feet). Terminated due to excessive seepage, some boils, and seepage from spillway area.
- Spillway is capable of safely passing 49% of the PMF. PMF overtops dam by 1.1 feet

Seismic
- Liquefaction/deformation hazard of foundation materials
- Seismic sources are capable of creating large ground motions at Martis Creek Dam

Remediation concepts
- Hydrologic is easy – widen spillway
- Seepage: Cutoff wall, Lower spillway invert, etc…are being considered
- Seismic: likely very difficult and costly, various methods are being conceived


6.4 Hidden Dam

(Courtesy of Ron Rose, USACE)

One of problems in this dam is seepage issue. Seepage areas and quantities have generally been on the increase with every inspection and also noticed by project staff. Now, urgent seepage study and spillway adequacy study is going on.

(Courtesy of Ron Rose, USACE)

6.5 Black Butte Black Butte Dam

(Courtesy of Ron Rose, USACE)

Hydrologic
- Spillway can only “safely” pass 78% of PMF
- Full PMF overtops entire dam by 1.0 feet

Seismic
- Seismic sources are capable of creating large ground motions at Black Butte Dam (~1g)
- Foundation judged to be liquefiable, and possibly portions of the embankment screened in 2005

More detail study is going on now.


6.6 New Hogan Dam

(Courtesy of Ron Rose, USACE)

One of problem in this dam is major earthquake source exists nearby. And fundamental study is being developed now.


6.7 Farmington Dam

(Courtesy of Ron Rose, USACE)

Farmington dam has a problem of excessive underseepage. This dam body has a pervious layer bounded by impervious embankment and relatively impervious substratum. It has a record of flood in 1998 and poor performance of embankment and foundation. At that time, damage to the upstream face due to wave action occurred, and downstream underseepage and boils made people practice flood fighting.

(Courtesy of Ron Rose, USACE)

Currently, more detail investigation is being done.