Figure 1. Clamshell Dredging Operation Underway

Dredging refers to excavating sediments under a water body. The purpose for each dredging operation varies, but the primary purpose of dredging is navigation channel deepening. Other purposes include construction activities, removal of contaminated sediments, removal of sediment buildup within a reservoir, altering drainage paths to control excessive flow, etc. Dredging activity can cause significant impacts to the subject water body in both the long and short term, so modeling dredging impacts on hydrodynamics, water quality, salinity, and sediment transport is important.

Current mathematical models can simulate the “before” and “after” effects of dredging, but they cannot provide a continuous simulation during the dredging process, so until now, the effect of a dredging operation could not be evaluated in a single model run. To address this issue, DSI recently developed a feature to simulate the sediment dredging process.

In this post, we will present this newly added feature by demonstrating salinity intrusion in a channel during the dredging operation. Salinity changes directly affect the river habitat environment, so it is crucial to model its effect during the planning phase.

DSI developed a bathymetry field file for EFDC+ allowing users to specify temporal bathymetry changes during the model simulation. The bathymetry field file, like a pressure field file, gives the user control over each individual cell during the model run period. Users can adjust the bathymetry by raising or deepening at a specific time and location. This additional feature allows the modeler to create a long-term simulation that includes a dredging operation, whether it be a one-time event or a periodic maintenance event; this can now all be done in one single simulation.

In our demonstration, we built a simple straight river with an ongoing dredging operation; the characteristics of the channel and the dredging plan are described in Figure 2