Assessing What Lies Beneath
For U.S. Coast Guard Base Kodiak, finding the best information for what utilities are buried underneath a given location no longer requires a time-consuming search through many incomplete and contradictory files.
By Mark C. Siegenthaler, P.E., PLS, M.SAME, and Laura W. Kelly, P.E.
U.S. Coast Guard Base Kodiak, Alaska, is the largest Coast Guard installation in the country. Until recently, records of its utilities, especially those constructed before 1990, were often incomplete or missing. Coast Guard Civil Engineering Unit Juneau sought development of a program to integrate a mapping system for the base with comprehensive databases of utilities and road infrastructure. PHOTO BY MARK SIEGENTHALER
U.S. Coast Guard Base Kodiak, located on Kodiak Island in the Gulf of Alaska, is the largest Coast Guard installation in the country. Managed by District 17, the base employs 3,500 people and provides support services and housing for 1,000 uniformed personnel and their families. It is homeport to three cutters, an airport, and hangars for five C-130 planes and six HH-60 helicopters. In addition, the base provides utilities for 14 outside agencies and commercial users, including Kodiak Benny Benson State Airport.
Utilities at Base Kodiak date back to World War II. Records, however, particularly of utilities constructed before 1990, often had been contradictory, incomplete, or missing. While paper drawings and other records of older projects were photocopied and saved as electronic files, and more recently, AutoCAD design drawings retained in a file storage and retrieval system, a single database containing a repository of the best knowledge for each utility simply was not available. The impact could be felt in mapping errors and delays in responding to emergency repairs.
Finding the best information for a given infrastructure component required an often lengthy search through many files. Even then, the data was restricted to physical properties—such as location, material, depth, size and age. Records frequently were incomplete, unverified or contradictory.
Effective management of drinking water, sanitary sewer and stormwater utilities requires detailed knowledge of system components, including material, size, age, condition, and functional adequacy. For water supply and distribution systems, adequacy of fire flows, water leakage and potable water quality are of primary concern. For sanitary sewers, maintaining adequate flow capacities to meet flow demands, and reduction of infiltration and inflow are major concerns. With stormwater systems, prevention of flooding and maintenance of water quality of the receiving waters are primary objectives.
For all of these, effective management, including routine maintenance and efficient planning of system expansion, is facilitated through an up-to-date, comprehensive database that includes modeling of the utility systems. Coast Guard Civil Engineering Unit Juneau sought development of a program for Base Kodiak that would integrate a mapping system with comprehensive databases of utilities and road infrastructure.
NEEDING A BETTER SYSTEM
For Base Kodiak, the optimum solution would be to have system inventory information (verification records, maintenance and repair history, condition assessments and the physical attributes of components) readily available in a single database that could be updated and used as a tool for managing repairs, maintenance and planning future projects. Hydraulic models of the water, sewer and stormwater systems were needed as well in order to be useful for assessing the performance of the base’s existing utility systems, and to plan and evaluate the designs of future improvements,
A geographic information system such as ArcGIS provides a ready platform for recording and accessing component attributes and their locations. However, base engineers and contractors prepare construction plans using AutoCAD. Software to model the hydraulic performance of the system needed to be accessible using AutoCAD, but also contain the data attribute capabilities of a geographicinformation system database. WaterGEMS and SewerGEMS by Bentley Systems were selected to model the water distribution system and stormwater and sewer systems.
These programs can be run within AutoCAD and store attribute information. For example, if a water pipe is selected with the cursor while running WaterGEMS within AutoCAD, then a list of attributes for that pipe appears, such as pipe diameter, pipe material, date of installation, reference project number and hydraulic roughness.
Bentley WaterGEMS model shown for the existing water system (left) and a proposed system with a 10-in connecting main joining two housing subdivision areas (right). The green, blue and magenta lines indicate higher flows; the yellow, orange and red indicate lower flows. The preponderance of magenta and blue mains shows the expected improvement in flows resulting from the connecting pipe. The Coast Guard used this information to justify installation of a new water main segment, which improved flow as expected. IMAGES BY LAURA KELLY
UTILITY INVENTORY MODELS
To create accurate models of the base water, sewer and stormwater systems, an intensive data inventory program was undertaken. Assemblages of drawings and other records along with anecdotal evidence was compiled and compared. Hierarchies were developed to give priority of acceptability, in a descending order of acceptance: surveyed, as-built, valve book citation, design drawing, existing facilities drawing, inventory drawing, and piping shown in previous utility system models.
Site reconnaissance was performed to verify locations of surface features and measure-down depths. An estimated 10 percent of water mains and valves were found to be located significantly differently than indicated on available mapping. About 5 percent of sewers and storm drains also differed enough from mapping as to impact their performance. Once up-to-date inventory models were created, hydraulic models of the water, sewer and storm systems could be developed, verified and calibrated.
For the water supply and distribution system, this required conducting fire hydrant tests to obtain pressure and flow values under known storage tank and pump discharges from the water treatment plant. For the storm system, drainage sub-basin runoff quantities were calculated for design storm events, such as the 10-year and 25-year storms. Peak flow rates based on occupancy or facility fixture units were developed to generate demand flows.
Following the completion of the WaterGEMS and SewerGEMS models, pipe replacement prioritization matrices were developed. Rating systems then ranked pipe, fixture and manhole replacement priorities based on factors including age, material, visual condition where accessible, failure history of similar and nearby pipes, and pipe importance.
REALIZING THE BENEFITS
The entire project, including inventorying and modeling, was a two-year effort completed in 2013. Base Kodiak has accrued a number of beneficial impacts.
For the water system, base engineers can now provide consultants with basis of design quantities for fire flows and pressures. Locations with inadequate fire flows are readily analyzed and the effectiveness of proposed system improvements are economically evaluated with the potential for substantial improvements in system performance and/or savings in project costs. In its first year of application, the water model was used to justify the need for a new water main connecting separate housing areas with a segment that significantly enhanced looped flow characteristics. Since completion, water model runs have been performed in the project development and design phases to evaluate existing and proposed system flows and pressures for new housing, aircraft hangar fire suppression systems, and to improve service to existing buildings.
A major benefit of the inventory system is the coordination of projects, including road pavement replacement. Graphics allow users to overlay utility replacement priorities with road pavement repair priorities so cost effective combined replacement projects can be planned.
Another significant benefit is the ease of component identification. Water main breaks occur with some frequency on the base. The facilities maintenance contractor requires immediate information on what has broken, so the proper materials can be brought to the site, excavation depth can be estimated, and the nearest isolation valves can be located and shut off. Now through the base’s WaterGEMS model, this information is available right away for the repair crew.
The infrastructure databases and utility models for Base Kodiak are proving useful in condition assessment, planning and design, and maintenance and repair—achieving both cost savings and improved system performance.