Many parameters must be monitored and significant data recorded to ensure safe operation of a dam. A new software system designed to monitor and store data related to dam safety, now being rolled out in 47 U.S. states, could be useful to concerned hydroelectric project owners and operators.
By Larry W. Caldwell, Joseph P. Scannell and Noller Herbert
As storms, floods, and other large weather events can place those living near a dam at risk, proper monitoring of a dam during such events is an important aspect of dam operation and maintenance. A new technology, currently in the testing and implementation phases, may prove beneficial by equipping plant owners and operators with real-time information about a weather event and its impact on the infrastructure affected.
Technology for dam monitoring
In 2011 and 2012, the Oklahoma Natural Resources Conservation Service (NRCS) and Oklahoma Conservation Commission partnered with USEngineering Solutions Corp. of Hartford, Ct., to implement DamWatch®, a software system designed to monitor and store data for 2,107 watershed dams in Oklahoma. NRCS is funding the project as a national pilot for a web-based information system for watershed dams.
A typical watershed dam is an embankment dam that has a conduit for discharge of smaller storm flows and a vegetated earthen open spillway to convey large storm flows safely around the dam. The primary purposes of watershed dams are generally flood control, water supply and grade stabilization. The majority of these watershed dams are located on private lands that are under easements with sponsors in the watershed, usually local conservation districts. Sponsors are responsible for operation and maintenance of the dams. The dams were planned, designed and constructed with assistance from NRCS.
Although watershed dams are typically too small to support the function of hydroelectric facilities, the overarching features of the DamWatch system - including the storage and retrieval of basic design, construction and operation information; hydrologic alerts; and maintenance tracking - are directly applicable for all dams, regardless of size or purpose.
DamWatch is a web-based software monitoring system that allows sponsors, those entities responsible for operating and maintain the dams, and NRCS personnel to monitor these dams in real-time and respond to potentially destructive flood events. The system gathers and archives real-time rainfall and stream flow data from sources such as the National Oceanic and Atmospheric Administration, National Weather Service (NWS) and U.S. Geological Survey (USGS) and compares rainfall data with site-specific thresholds of dam capacity and then alerts staff of potential spillway flows at dams.
DamWatch incorporates automatic messaging that alerts users through cell phones, pagers, fax messages, e-mails or other means. Users can monitor these messages during critical flood events and dispatch staff as needed to those dams for which alerts were issued.
DamWatch also stores site-specific data, such as inspection reports, as-built drawings, operation and maintenance agreements, emergency action plans (EAP), photos and videos. These data can be accessed remotely, allowing quick interaction between on-site personnel and specialists in multiple offices.
As a result of the success of the Oklahoma pilot project, a national contract was awarded in September 2012 to USEngineering Solutions for implementation of a similar system to monitor about 11,700 watershed dams in 47 states and one U.S. territory.
USDA Watershed Program
Since 1948, NRCS has assisted project sponsors with the construction of more than 11,700 watershed dams in 47 states and one U.S. territory, with assistance from the following USDA Watershed Program authorizations: Public Law 78-534, Public Law 83-566, Pilot Watershed Program and Resource Conservation and Development.
These dams are locally operated and maintained by project sponsors with some federal assistance, which includes planning, design and construction of the dam, as well as technical assistance to investigate operation and maintenance problems and recommend solutions. Sponsors are generally local conservation districts, special-use conservancy districts or municipalities that have easements on private lands where the dams are located. In almost all cases, sponsors have non-technical personnel in charge of the operation and maintenance of the dams. Most sponsors rely on NRCS for technical assistance.
Oklahoma has been a national leader in the USDA Watershed Program since the program's inception in 1944. The state has many national-watershed firsts, including the first watershed dam built (Cloud Creek Watershed dam no. 1 near Cordell) and the first watershed dam rehabilitation (Sergeant Major Creek Watershed dam no. 2 near Cheyenne). Since 1948, 2,107 watershed dams have been built in Oklahoma (see Figure 1), more than in any other state in the nation. In 2012, more than 650 of these watershed dams reached the end of their 50-year design life, making Oklahoma watershed dams the oldest in the nation.
Typically, Oklahoma watershed dams are earthen embankment dams ranging from 20 to 80 feet high, with earthen vegetated spillways and concrete or metal-principal spillways. Most of the dams were designed primarily for flood control, grade stabilization, water supply or recreation; therefore, they typically do not store much water except for short periods immediately after large storm events. Most are in remote areas.
Dam owners and watershed program staff have compiled large numbers of records and data that provide valuable information during structural failure or large rainfall events. As-built drawings, operation and maintenance inspection reports, agreements and commitments made by sponsors and NRCS and original project work plans are all important to have on hand in case of an emergency.
Further, having access to a current EAP is critical for identifying and evacuating people downstream who are at risk when dams fail or flood. Each of the 229 high-hazard watershed dams in Oklahoma has an EAP.
From 2006 to 2010, Oklahoma NRCS staff scanned all the critical watershed records so they could be stored and accessed electronically. These records included more than 32,000 electronic files, and their size exceeded 13 gigabytes. The sheer volume of the information and ability to periodically update the information and make it available to multiple users at different locations made DVD or hard drive storage impossible. NRCS determined that a web-based software system with 24/7 accessibility would be the best way to store and retrieve the dam-safety information.
The DamWatch solution
Oklahoma NRCS developed a proposal to pilot the DamWatch system for two years. DamWatch empowers NRCS, project sponsors and emergency managers to leverage electronically stored dam-safety data with real-time data monitoring. The system is linked to NWS and USGS real-time precipitation and stream flow data that alerts staff and emergency personnel of predetermined site-specific thresholds. Upon receipt of alerts, personnel can use the system interface (see Figure 2) to determine if preventative actions or emergency responses are needed for potentially life-threatening situations, especially those involving high-hazard dams. The system also be used to conduct mock emergency events for EAP training.
Watershed sponsors need a system that allows storage and easy retrieval of vital dam records. This is especially important as the volume of data grows and dams age, and for providing information to new employees and sponsors who are not familiar with a particular dam.
The basic engineering and program data stored in the Oklahoma DamWatch system includes:
- As-built construction drawings;
- Basic design and other data contained in the National Inventory of Dams (NID) database, maintained by the U.S. Army Corps of Engineers;
- Emergency action plans;
- Current hazard classification data;
- Breach inundation maps;
- Operation and maintenance agreements;
- Project benefits (such as flood damages prevented by the dams, wetland enhancements, wildlife habitat improvements, and so forth);
- Assessment reports;
- Watershed project work plans;
- Photos and videos;
- Dam modifications or repairs; and
- Auxiliary spillway flow history.
DamWatch enables 24/7 real-time access to this information via the web by project sponsors, NRCS employees and emergency managers and other authorized users, as opposed to only those with the ability to get to an office and file cabinet drawers.
The DamWatch program uses geographical information system (GIS) technology to display a dam's location and drainage area. This system can collect and process any real-time data at regular intervals. These data can be compared against predetermined thresholds to alert essential personnel when a dam is experiencing a critical precipitation event.
The amounts of precipitation at specific locations can vary significantly when such an event occurs in an area where there are numerous watershed dams. Using NWS radar data, DamWatch can determine which dams have received the heaviest rainfall within a drainage basin and thus have the highest probability of spillway flow. This information allows project sponsors and NRCS to prioritize field inspections of the most critical dams first and allocate resources efficiently and cost-effectively. As DamWatch allows sponsors to concentrate on dams that received the highest amount of rainfall and thus the greatest need for attention, it saves time and money by avoiding the need to send staff to the lesser risk dams.
Users can remotely access DamWatch anywhere using any web-enabled device. In Oklahoma, six Motorola Xoom tablet computers were selected to test the ability of users to access DamWatch in the field. The tablets enabled personnel to remotely interact with the system to document activities, upload pictures or view online files. Each tablet had the capability to receive alerts, view online files, take photos and videos, and even video chat with other active field personnel.
The goal of establishing alert thresholds for DamWatch is to provide timely notice to users of possible or impending auxiliary spillway flows with special attention given to high-hazard dams. The storm rainfall amount (the estimated accumulated rainfall, continuously updated, since the last one-hour break in precipitation) detected by the NWS' Next-Generation Radar (NexRad) system, a network of 159 high-resolution S-band Doppler weather radars operated by the National Weather Service, is compared to the threshold amount establish for each dam. If an established threshold is exceeded in DamWatch, the system will issue a NexRad alert for that dam.
DamWatch uses a specific methodology to establish these thresholds. The designed-detention storage volume for each dam (as shown in the NID) is converted to watershed inches. The rainfall in the dam's drainage area needed to produce the runoff to fill the designed-detention storage volume is estimated using the project work plan runoff curve number. Two precipitation threshold levels are established for each dam, and each has a corresponding message in the alert to describe the situation, whether a rainfall alert or a spillway-flow alert.
Here is an example of an initial alert message from DamWatch:
There are some exceptions to this methodology. Multi-purpose dams may have much greater available detention storage if they were built for municipal water supply, recreation, or irrigation. This storage may not be fully used: this provides additional detention storage at the time of the storm. The methodology does not account for principal spillway discharge during a storm. Most times this will be minimal. Exceptions include: designed full-flow grade stabilization structures or dams with large principal spillway conduits. The methodology also does not capture situations where storms occur over several days. A revised methodology needs to be developed in the future to estimate principal-spillway discharge during the storm to deduct from estimated runoff value.
Expanded use and impact
The Oklahoma NRCS DamWatch system pilot proved to be a tremendous tool. It provided all the critical information needed during emergencies, as well as in normal day-to-day operation of dams.
During the summer of 2012, the NRCS national staff leadership decided to implement a dam-monitoring system for the 11,700 watershed dams in 47 states and one territory. NRCS issued a national solicitation in July 2012 for a competitive fixed-price, US50,000 contract. USEngineering Solutions was awarded the contract in September 2012. The contract term is one year, with four additional option years. The implementation period extends for six months after contract award.
This is a tremendous effort to implement a national system, gather the watershed data, load it into the software, train users and provide an operational system nationwide. The national system is now in the formative stages of implementation. By late spring 2013, the nationwide system is expected to be operational with all users trained and using the system by fall 2013.
While NRCS is not currently involved in any hydroelectric projects, the features of the DamWatch system are applicable to all dams, including those with hydroelectric turbines and powerhouses. Further, there have been discussions with owners of Federal Energy Regulatory Commission-licensed hydroelectric projects to use DamWatch for more effective operation and management of their dams.
Larry Caldwell, an engineer at the Oklahoma Conservation Commission, has led implementation of the Oklahoma DamWatch pilot project. Joseph Scannell, president of USEngineering Solutions Corp., is responsible for adapting the design of the DamWatch system for specific projects. Noller Herbert, director of the Conservation Engineering Division of the U.S. Department of Agriculture's Natural Resources Conservation Service, is responsible for leadership of the implementation of DamWatch for the USDA Watershed Program.