A detailed survey of a specific area (usually a 1 to 2 mile section) of the river. Dredge surveys can be split into two groups: pre-dredge surveys and post-dredge surveys. Pre-dredge surveys are analyzed to determine if dredging is required in a potentially problematic location. If dredging is required, these surveys are then used to layout the dredge cuts and to estimate the volume of material that will need to be moved. A post-dredge survey is completed after dredging has been completed in a specific location to ensure that the problematic area has been removed.
The Dredging Reference Plan (DRP) is intended to be used as a temporary replacement to the District's Low Water Reference Plan (LWRP) during the current extreme low water event. The DRP is based on an analysis of recent low water channel performance and is intended to provide a more accurate and consistent profile between the gages on the Middle Mississippi, using St. Louis as the main reference. The DRP is temporarily replacing the LWRP due to changes in the channel since the LWRP's last full re-calculation and acceptance. The plane was developed between each automated gage site based on recent low-water readings and shifted down to be defined as the plane correlating with a St Louis gage reading of -7.