The Corps maintains the navigation for over 25,000 miles of inland and intracoastal waterways and channels and more than 900 ports and harbors across the United States. The accumulation of sediment in these waterways—known as shoaling—reduces navigable depth and width and, without dredging, may result in restrictions on vessels passing through the waterways. These restrictions often apply to the vessels’ draft—the distance between the surface of the water and the bottom of the hull— which determines, in part, the minimum depth of water in which a vessel can safely navigate. Draft restrictions may result in delays and added costs as ships may need to off-load some of their cargo to reduce their draft, wait until high tide or until waterways are dredged, or sail into another port. These restrictions are imposed at times on various waterways throughout the United States due to shoaled conditions, which could disrupt the shipment or delivery of millions of dollars’ worth of cargo, according to Corps documents and officials. Maintenance dredging needs across these waterways vary significantly, with the majority of dredging occurring along the Atlantic and Gulf Coasts, according to Corps officials. A variety of dredge vessels and other supporting equipment are used for dredging, with variation in their sizes and capabilities, and the conditions under which they best perform. For example, mechanical dredges excavate and remove material by applying mechanical force to the material by means of an implement such as a bucket on the end of a cable suspended from a crane, and deposit the material on a barge for transportation to a placement site. Dustpan and cutterhead dredges, in contrast, are hydraulic dredges that use a pump and either a cutterhead or high-pressure water jets to erode material and remove it from the bottom of a waterway, and then transport the dredged material through a pipeline to a placement site. One of the largest dredge types, the hopper dredge, is a self-propelled ocean-going vessel that hydraulically dredges material and places it into the hold or “hopper” of the ship, where the material is stored while being transported to a placement site where the material may be released from the dredge into open water or pumped to a placement site. Dustpan and cutterhead dredges may work in shallower waterways and have the ability to maneuver in river traffic, whereas hopper dredges perform much of the dredging work in ports, harbors, and other coastal channels and waterways exposed to the ocean. Corps headquarters and its 8 regional division offices generally provide guidance and policy oversight to 38 district offices located throughout the United States (see fig.1). District offices are generally responsible for managing dredging projects located within their district boundaries, including planning, awarding, and administering maintenance dredging contracts with industry. The Corps owns and operates a small fleet of dredge vessels, but it relies mostly on contracts with industry for its maintenance dredging work. According to Corps officials, the Corps typically solicits fixed-price competitive bids from contractors. To help evaluate contractor bids, Corps district offices are to develop an independent government cost estimate for each contract solicitation. The estimates are to be developed using information on the costs of owning and operating dredges—such as acquisition, fuel, labor, and shipyard costs—along with the project information for which the dredging is needed—including the amount and type of material to be removed, the distance from the dredging site to a placement site, and other factors that affect productivity such as environmental requirements. In soliciting bids from contractors, Corps districts have most commonly used a sealed-bid process, resulting in a fixed-price contract between the Corps and the contractor, with the contract generally awarded to the lowest responsible bidder with a responsive bid that is no more than 25 percent above the government cost estimate. Corps officials noted that if the Corps uses a solicitation type other than sealed bidding, Corps districts generally have flexibility in determining the specific contract type to employ for their projects, and may choose other types, such as an indefinite delivery, indefinite quantity contract. An indefinite delivery, indefinite quantity contract is a type of delivery contract that provides for an indefinite quantity of supplies or services within stated limits, during a fixed period. The basic cost components of a maintenance dredging contract generally include (1) mobilization of the dredge and related equipment to the dredging site; (2) utilization of the dredge and related equipment to conduct the dredging, as well as other project-specific activities required under the contract, such as environmental monitoring; (3) transport of the material to a placement site, which can include among others, open water placement sites, confined placement facilities, or beneficial use sites, such as for building a wetland or renourishing a beach; and (4) demobilization of the dredge and related equipment. Each dredging project is unique and a number of factors influence the cost of these components across projects, including the type and quantity of material to be dredged, allowable locations for placement of material, timing, environmental requirements, and the location and weather conditions where dredging occurs. Much of the maintenance dredging the Corps undertakes is cyclical in nature, with dredging needed annually or every few years, according to Corps officials. A limited number of companies have conducted the majority of maintenance dredging contracted by the Corps. Industry data provided by the Dredging Contractors of America indicate that nationwide, during fiscal years 2004 through 2013, an average of about 50 companies were awarded one or more dredging contracts by the Corps annually, though over 50 percent of the contracts, on average, were awarded to 8 companies. According to Corps and industry information, the ownership and operating costs of dredges often require large capital outlays to cover fixed costs such as equipment, insurance, and depreciation, as well as variable costs such as payroll for crews, fuel, and equipment repairs and upgrades—and therefore it may be difficult for companies to quickly enter the dredging market. Through its dredging database, the Corps maintains data on its dredging projects, including all maintenance contracts. Information in the database is used for a variety of purposes, including tracking anticipated and actual project scheduling information, and tracking information across contracts on anticipated and actual contract costs and quantities of material dredged. For each contract, the dredging database includes data elements to capture information on the project name, status, dredging location, government cost estimate, type of contract, type of dredge used, number of bidders, winning bidder, bid amounts, estimated quantities of material dredged, and final contract costs and actual quantities of material dredged after the contract is complete. The database also contains data elements for specific cost components, such as mobilization and demobilization costs, as well as data on the location and types of placement sites used. District offices are responsible for entering data into the database for the contracts they manage, and the database is overseen by Corps headquarters. Cost data in the Corps’ dredging database are unreliable and, therefore, the total costs of maintenance dredging contracts during fiscal years 2004 through 2013 are unclear, but Corps officials report that multiple factors likely contributed to cost changes during this period. The Corps relies on data from its dredging database for assessing trends in maintenance dredging contract costs over time, among other things, but we found that many of the records in the database did not contain information on final costs or actual quantities of material dredged. Corps headquarters officials said they review some data in the dredging database monthly and generally notify district offices when they identify errors or omissions, but corrections may not always be made by the districts. We found that Corps districts do not have systematic quality control measures in place to ensure the data are complete and accurate, but rather the district offices have taken various approaches to entering cost and cost-related data into the database. Through our interviews with Corps officials and review of a sample of projects, we found that multiple factors—such as the level of competition for contracts and the need to comply with environmental requirements—likely contributed to changes in maintenance dredging contract costs during the period of our review. The total cost of maintenance dredging contracts during fiscal years 2004 through 2013 are unclear because data in the dredging database are unreliable. Specifically, of the 1,405 contract records in the database that were marked as “complete,” we found that about 19 percent (264 out of 1,405) did not contain information on the final contract costs or the actual quantity of material dredged. In addition, for those 1,141 contract records marked complete that had final contract cost and actual quantity information entered, we found instances where other related contract information was incomplete, including the following: About 20 percent (224 out of 1,141) of the records did not contain a contract number, contractor identification number, or contract award date, raising questions about the validity of these records overall. About 7 percent (75 out of 1,141) of the records did not have costs for mobilization and demobilization specified, and it was not clear whether these cost components may have been entered into the database. We also identified anomalies that raised questions about the accuracy of some of the cost and cost-related information in the database. Specifically, in analyzing the data to determine the cost per cubic yard of dredging during fiscal years 2004 through 2013, we found wide variation, with the cost per cubic yard ranging from $0.03 to $1,736, with an average cost of $16.08 across the 1,141 records marked as complete and with final contract cost and actual quantity information.