RD257 - Costs, Funding and Prioritization of Virginia Dams to Meet Minimum Public Safety Standards - October 2011


Executive Summary:
*The Executive Summary and Report were replaced in their entirety by the Department of Conservation and Recreation on December 22, 2011.

Introduction

The purpose of this analysis was to identify dams in need of repair and estimate the costs to meet the public safety standards established by the Dam Safety Act § 10.1-604. The report includes estimated costs for high and significant hazard potential dams. Given that the availability of funding for dam improvements varies depending on ownership, dams were classified by owner group into dams owned by the state, by Soil and Water Conservation Districts, by local governments, private entities, and utilities. Preparation of the Report was directed by Item 351N of Chapter 890 of the 2011 Virginia Acts of Assembly. (*1)

The Department of Conservation and Recreation is responsible for assisting dam owners to maintain their dams to prevent failures, and to protect lives and property as authorized by the Dam Safety Act § 10.1-604. The Department assists owners and engineers with more than 1600 dams in Virginia. In addition, the Department assists 285 localities with management of their floodplains.

In order to improve dam safety and assist dam owners, the Department of Conservation and Recreation (DCR) is implementing a series of initiatives. In 2012, DCR will execute a contract to provide a Dam Break Early Warning System. The warning system will collect data from live sources such as the National Weather Service (NWS), National Oceanic and Atmospheric Administration (NOAA), Natural Resources Conservation Service (NRCS), and the U.S. Geological Survey (USGS). Alerts and notifications will be distributed immediately to dam owners and emergency responders through electronic media according to DCR defined specifications or plans of action. There are actions that can be taken to prevent a dam failure. For example, lowering the water level behind the dam prior to a heavy storm increases the capacity and may prevent a failure. Another initiative, the dam first aid initiative, will allow DCR to equip trailers with siphons and pumps to provide emergency repairs to dams. The trailers will be equipped and located throughout the state to provide equipment to dam owners to make emergency repairs and prevent a potential dam failure.

To assist dam owners in operating and maintaining their dams and complying with the Dam Safety Act and Impounding Structure Regulations, a Dam Owner’s Handbook was published in December 2010. To date, 750 copies have been mailed to dam owners throughout Virginia and distributed in-person, to dam owners and consultants, at training sessions, the 2011 Virginia Water Conference, and 2011 Environment Virginia.

A new E-Newsletter will provide an inexpensive means to communicate regularly with all DCR Dam Safety and Floodplain Management stakeholders. Updates to the law, regulations and guidance, grant announcements, training programs, and success stories can be shared with stakeholders. The first E-Newsletter was distributed in April, 2011. The second E-Newsletter informing dam owners what to do after the earthquake and to prepare for a hurricane was sent on August 25, 2011.

On May 24, 2011, the Soil and Water Conservation Board approved three fast track actions directed by the General Assembly to assist dam owners and improve the Impounding Structure Regulations:

i. Incorporate the consideration of low traffic volume roads into the hazard classification. Existing guidance on roadways on or below impounding structures will be the basis of this revision to the regulations;

ii. Develop a simplified methodology for dam break inundation zone studies and mapping to provide a low cost alternative for dam owners for determination of low hazard potential classification and eligibility for the general permit;

iii. Develop a general permit for owners of low hazard potential dams.

Dams provide water supply, flood control, hydro-electric power, agricultural resource, irrigation, recreation, fish and wildlife habitats, and contribute to water quality. Virginia is divided into five dam safety regions. Each region is assigned a dam safety engineer. A common goal shared by all is maintaining dams to meet minimum public safety standards for the prevention of dam failures. Dam owners are responsible for lives and property, including the dam itself, in the event of a dam failure. The biggest challenge for dam owners in Virginia is the costs of maintaining dams in a safe condition.

Stakeholder Involvement and Data Collection

Upon receiving direction to conduct this analysis, DCR contacted stakeholders, including dam owners, localities, Soil and Water Conservation Districts, engineers, contractors, other state agencies and federal agencies, by mail and email to explain the purpose of the report and to request cost data on dams (Table 1). 1264 surveys were delivered by mail to dam owners requesting cost estimates for planned dam rehabilitations and cost data for previous rehabilitations. 79 of the 1264 surveys were returned, for a 6% response rate from dam owners. 732 reminders were sent by email to dam owners with known email addresses and additional interested stakeholders. Information was received for about 10% of the known regulated dams throughout Virginia’s dam safety regions (Figure 1). Present and past cost information for the repair of dams was obtained from state agencies including DCR, DGIF, and UVA, and federal agencies including NRCS and FEMA.

2.1 Methodologies for Estimating Costs

Accurate estimates of repair costs for dams require detailed engineering analyses and design, construction drawings, specifications, and construction cost estimates. In order to obtain the cost estimates for this analysis, returned surveys and cost data from past and planned rehabilitations were analyzed. The estimated costs received from responding owners or their engineers were included in this examination for the specific dam provided for.

Cost benefit equations were developed to relate additional spillway capacity required to cost. This relationship offered a way to estimate the costs of dams for which no owner estimates are available. In addition, average costs for dam repair for each potential hazard classification were extrapolated from known costs of past and planned repairs of state owned dams and owner estimates. The equations were used to estimate the cost of repairs for dams without owner estimates or accurate information on the required spillway capacity. In addition, Regional Dam Safety Engineers checked and adjusted the resulting cost estimates based on their knowledge of the dams from inspections, review of information provided by dam owners and their engineers, and data on each dam recorded in the dam safety database.

The estimated cost to repair each dam was determined for each hazard classification and for dams owned by the state, Soil and Water Conservation Districts, local government, private entities, and utilities. The highest priorities for repair are high hazard dams, followed by the second priority, significant hazard dams, and last, low hazard. It has been determined that, as to low hazard dams, DCR needs only to know they exist in order that they are not inadvertently converted to significant or high hazard dams by development.

2.2 Methodology for Prioritization of High Hazard Dams

High hazard dams put the greatest amount of property and lives at risk, while at the same time yielding the most protection, in dollars spent. The prioritization and the identification of these dams in need of repair are critical in the protection of life and property. The prioritization methodology considered the number of people at risk should a dam fail, cost to repair, and the change in probability before and after the fix for overtopping and piping failure modes. The methodology is expressed through cost benefit equations. These equations will be provided upon request.

High hazard dams were prioritized by owner group because funding sources may be different for each. The owner groups are: dams owned by the state; Soil and Water Conservation Districts; local governments; private entities; and utilities. Available sources of funds for dam repair include state bond money to repair park and district dams. Dams were selected for repair by a prioritization process based on high hazard classification and number of people at risk in the event of dam failure.

Discussion of Prioritization & Cost Estimates

A. High Hazard Dams

The prioritization for high hazard dams was determined by an analysis of failure modes, estimated cost of rehabilitation, number of people downstream, and cost benefit analysis. The lowest number calculated for the prioritization factor indicates the highest priority dam for repair and is listed first in Tables A1-B5 in the appendix.

The total number of high hazard dams was 221 and of those 104 dams either meet minimum public safety standards or money is already allocated for their repair. Virginia has 117 high hazard dams in need of repairs to meet minimum public safety standards. Of those twenty-one are owned by the state, 37 by the SWD, 23 by the local government, 33 are privately owned, and three are utility owned. The total estimated cost for each owner group is:

State Owned (21): $21,399,619
SWCD (37): $62,590,242
Local Government (23): $36,713,402
Privately Owned (33): $41,789,763
Utility (3): $5,174,208

Significant Hazard Dams

The total number of significant hazard dams was 398, and of those, 75 meet minimum public safety standards or money is already allocated for their repair. Of the 399 significant hazard dams, 323 are in need of repairs. Of those, ten are owned by the state, fourteen by the SWCDs, 28 by the local government, 267 are privately owned, and four are utility owned. The total estimated cost for each owner group is:

State Owned (10): $17,374,976
SWCD (11): $14,920,953
Local Government (28): $58,435,535
Privately Owned (266): $323,612,385
Utility (4): $9,602,094

The prioritization of high hazard dams for repair was determined by an analysis of failure modes, number of people downstream, and estimated cost of rehabilitation. The two failure modes analyzed are: i) dam overtopping; and ii) seepage through the dam. The number of people downstream from a dam was estimated from existing dam break inundation analysis, maps, and emergency action plans. Estimated cost of repair was obtained from the owner or, if not available, was determined using the formulas described earlier in this report. Because the cost of dam repair depends on the difference between the existing spillway capacity and required spillway capacity, a formula was developed from costs for past dam repairs that relates cost to repair dams and additional spillway capacity. For each high hazard dam the estimated cost of repair is calculated from the formula based on the known spillway capacity. The lowest number calculated for the prioritization factor indicates the highest priority dam for repair and is listed first in the following tables for high hazard dams. Although there is no way to know the actual risk of dam failure, engineering estimates of the probability of dam failure based on condition are used in the prioritization analysis.

Several assumptions were made when conducting the foregoing analysis. The prioritization analysis focuses on evaluating the impact on people downstream but does not include the impact on property downstream. Although numerous dam failure modes are possible, only the two most probable failure modes, overtopping and piping were analyzed. (*2) This estimated cost to repair dams in Virginia is based on analytical methods to obtain the best estimates possible. With increased efforts and experience with the repair and improvement of the safety of dams, greater accuracy in estimated costs will be possible.
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(*1) By an amendment to the budget (Item 351 N.), DCR was directed as follows: “It is the intent of the General Assembly that based on the Commonwealth's commitment to safe dams in Virginia, the Department of Conservation and Recreation, with cooperating agencies, shall evaluate the costs to repair regulated dams owned by the state, Soil and Water Conservation Districts, local governments, and the private sector in order to upgrade them to state safety standards. A prioritization of known high hazard dams in need of repairs to meet minimum safety standards based on hazard to life and property from a dam failure shall be considered. The results of the evaluation shall be submitted to the Governor and the Chairmen of the House Appropriations and Senate Finance Committees by September 30, 2011."

(*2) The impact on people downstream in piping failure is estimated to be 1/3 of the impact in PMF failure. Probable Maximum Flood (PMF) is the flood that might be expected from the most severe combination of critical meteorologic and hydrologic conditions that are reasonably possible in a region. The PMF is derived from the current probable maximum precipitation (PMP) available from the National Weather Service, NOAA. The annual piping failure probability is based on dam condition. If the dam condition includes several seepage or wet locations that may cause a probable piping failure, the probability for piping failure is 0.01/year. The return period under these conditions is 100 years. If the dam condition has no seepage or wet locations, the probability for piping failure is 0.00001/year. The return period for condition is 100,000 years. A 100-year flood represents the flood magnitude expected to be equaled or exceeded on the average of once in 100 years or a return period of 100 years.