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• Board Meeting Date: 5/23/2007
• Description: IWMD Section - Water Supply Reserve Account May 2007 Grant Allocations
• Board Meetings - Doc Type: Memo

storage capacity is also included with this supplement. Generally, the needs can be placed in one of the
following categories, in this order of priority:

1. Outlet W orl(s - Deterioration of outlet components such as pipes and gates is one of the greatest
safety and serviceability concerns for all dams, particularly older ones which may have un-protected
steel pipes. Erosion and removal of embanl(ment or foundation material along the outside or into and
through the pipe can result in sudden catastrophic failure even for dams that have had a long history
of stability. Additionally, the risl( is increased at some of the project dams which have downstream
control valves. Downstream valves pressurize the outlet pipe. Therefore, the proposed worl( includes
focusing attention on the outlet systems for all of the dams.

2. Seepage - Uncontrolled seepage, particularly seepage which exits on the embanl(ment, at the
embanl(ment/foundation contact, in the foundation slightly downstream from the toe of the
embanl(ment or along the outside of the outlet pipe, is of a concern. If the seepage forces or pressures
are great enough, material can be eroded from the embanl(ment or foundation, or the pressures can
de-stabilize the dam slopes. Methods to address seepage range from channeling and measuring to
installation of filters and drains. The proposed worl( includes identifying significant seepage areas.

3. Slope Stability - As experienced with the Carl Smith failure, a long history of embanl(ment stability
does not assure either perpetual security or adequate safety factors under all possible conditions.
Slope stability is affected mainly by the steepness of the slopes, the characteristics and strength of the
embanl(ment and foundation soils and the seepage forces and pressures. In order to adequately
address slope stability issues a considerable amount of worl( is needed including drilling test holes
through the embanl(ment and foundation and installing and monitoring piezometers. That degree of
effort is considered well beyond the scope of worl( needed to prepare the proposed inventory.
However, it is possible to perform a preliminary stability analysis using soil samples from shallow
hand-auger holes and based on observations of downstream surface seepage. The proposed project
includes this preliminary level of stability evaluation.

4. Spillway/Flood Hydrology - Except for transient maintenance-related issues such as debris and ice
accumulation, a long history of spillway adequacy can indicate some degree of spillway security.
Therefore, this is the lowest priority item and related aspects of the proposed study will be limited to
field observations of spillway conditions, identification of spillway adequacy modeling previously
performed by the Division of Water Resources, and research of typical means used to identify
spillways that are susceptible to ice damming and effective means used to control ice damming.
Future investigations may pursue this aspect of the facilities at a more detailed level. If, at some
future point, it appears appropriate to pursue spillway and flood hydrology issues in a more
comprehensive manner, it would be best to evaluate the entire basin rather than individual dams.
This is because spillway considerations can be substantially impacted by both upstream and
downstream dams. For example, a small dam may not pose a great breach hazard if a larger
downstream dam could contain the entire capacity of the smaller dam within its freeboard. On the
other hand, a dam which has adequate spillway capacity when considered by itself may pose a much
greater hazard if the breach of an upstream dam creates a cascading series of breaches in this dam
and, perhaps, other downstream dams. A comprehensive evaluation would lil(ely consist of creating
a flood hydrology model of the entire basin that could be used to evaluate the impact of a wide range
of precipitation events.

5. General Dam Condition - Overall characteristics of the dam and appurtenant features which are
relevant to safety and serviceability will be observed and noted.

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