Central Gate Opening for Removing Sand Bar on Middle Channel April 6

Current Opened Gates: #1 (partial), #17~22

Gates #17 ~22 were opened to remove sand bar placed on middle channel. Gates were set 3.5 ft water depth and 3.0 ft was measured on PLC screen.

Sand bar placed middle channel has been disappeared, while water depth has been decreased. However, sand bars were found almost everywhere of the upstream (Figures 2 & 3).

Figures 2 and 3 show sand bars formed at entry of the fish passage and at upstream of the west side of the channel, respectively. Faster flow velocity was measured (2.5 ft/s at

channel center) than partial gate opening task. With the central gate opening, sand bar placed on middle channel has been surely disappeared, but it seems that the sand bars

relocated (or spread out) just near by the original location, not washed away through the opened gates.

Interesting sand bar shape and placement was captured on 12-March by the aerial photo. Click the figure for large image. The aerial image geo-referencing is in progress and will be used to investigate sand bar movement and volume changes.

No sediment depositions were found at right behind gates except gates # 7-9 (Figure 1). However, very shallow water depth, in other words, high sediment depositions were found

downstream of the gate opening area (gates #17~22) as shown in Figure 4.

Sediment deposition at the north intake bay was removed completely (Figure 5). Another erosion was found at the fish passage entry as shown in Figure 6.

Gravels were eroded and fine sand was revealed.

Drift velocity vector mapping measured from kayak of upstream pool for the central gate opening configuration is in progress.