EEMS Feature: Partial Flow Blocking

Partial flow blocking was added as a feature of EEMS with version 10.1. This capability simulates partially blocked vertical depths caused by floating objects such as ships and bridges. Using this option, other submerged features, such as baffles and submerged weirs and structures, can also be modeled in EFDC+. The partial blocking option influences flow, constituent transport, particle tracking, and wave action. As part of testing this feature, we modified a 2-D salinity tank model as described below. Furthermore, to demonstrate the application of partial flow blocking in a realistic situation, we also updated our Lake Washington to include the 520 Bridge, a four-lane floating transport bridge carrying traffic between Seattle and the Eastside.

2D- Tank Salinity Induced Currents with Baffles

This example model is a modification of the classic density current 2D-tank experiment. Here, a 2 m long by 0.5 m high tank with floating and fixed baffles (shown as heavy black lines) was initialized with 30 parts per thousand (ppt) salinity on one side and 0 ppt salinity on the other. As soon as the simulation begins, baroclinic forcing causes a rapid redistribution of the salinity. The animation shows a vertical slice through the tank as the salinity redistributes and mixes.

Floating Bridge on Lake Washington

Lake Washington is located adjacent to the city of Seattle in Washington State. DSI built a real-time model to simulate temperatures in this very deep lake. Because of depths over 65 m in some places, construction of conventional bridges over the lake has been difficult. For this reason, a number of floating bridges have been constructed, with the one from Evergreen Point (520 Bridge). This bridge has a floating span length of 2.35 km (7,710 ft) and a width of 35 m (116 ft). This makes it both the longest floating bridge in the world, as well as the widest. The draft of the bridge is approximately 2.5 meters below the water surface. The 520 Bridge effectively stops floating objects and wind-generated wave action from passing under it. To simulate this phenomenon, our EFDC+ model of Lake Washington was modified to add the floating bridge blockage. To simulate the effect of the floating blockage, we simulated Lagrangian particles. Four particle groups were initialized at two different depths north of the bridge and two different depths south of the bridge. Particles released at the depth of 1.5 meters should be largely blocked by the bridge, and those released at 4.5 meters could be transported under the bridge. This behavior is evident in the accompanying animation.

You can download this floating bridge simulation of Lake Washington and run it with the EEMS in the demo mode, for free.