Hello, I am looking for approaches to flood control for the Skagit Valley, Washington State.
The Skagit River comes down from the Cascade mountains to Puget Sound; its watershed defines Skagit County. There are towns iand small cities build along the Skagit River as it winds down the valley to the delta on the "flats".... how do we plan and design for the flooding that occurs in this valley?
Currently there are plans to build a flood wall to keep the water out of the city of Mount Vernon, which is right on the banks of a curve in the Skagit River. What will nature actually do, where will the water go, in a hundred-year flood? (Or a twenty-year flood, or an annual flood?) City, county, federal agencies are working on a flood protection plan. They are debating how high a 100-year flood will "really" be.
I would like to garner expertise from people who can evaluate the options and make specific recommendations on how to protect the cities, towns, and farmland in the river's path. I am looking to "think outside the banks" on this issue. Thank you!
Flood prevention for Skagit Valley
That is a tough issue. There are many factors involved: politics, economics, hydrology, social issues, environmental issues, etc.
The best place to start is efficient/effective stormwater management at a site scale. By this I mean, addressing stormwater/melt water on a small scale, i.e. many small systems vs a few large systems. Implement stormwater Best Management Practices (BMPs) at developed (sub)urbanized areas. Choose BMPs that reduce peak flow and volume. The goal here is to reduce the amount of water entering the stream/river from developed areas, try to recharge groundwater and use BMPs to control the timing of the water. Furthermore the goal with BMPs are to minimize the impacts that our developments have on stream hydrology. However, even with these measures rivers will flood, it is a natural process. The is nothing unusual about flooding, and it isn't necessarily a problem, until we build something that we don't want to flood. The best option is not to build in flood prone areas, however flood-prone areas are often developed.(e.g.New Orleans)
There are many techniques and practices to effectively handle stormwater from urban, suburban and rural areas. These practices should be implemented at all new developments and can be retro-fitted into old developments. Addressing new developments is somewhat simpler... regulations could require such practices. However retro-fitting is tough...who is going to pay for it? Which sites should be retro-fitted? Etc.
However stormwater from developed sites is just one piece of the puzzle. It may be the case that managing stormwater from developed areas is not sufficient to protect structures built on the flood plain. Now there are several options...move those structures, move the water or store the water. No one usually wants to move a building and no one wants to build a dam or a diversion. So what is left? Build levees and dikes. But there are still other options... diversions don't need to be canals, storage doesn't need to be dams, groundwater recharge zones could be constructed, underground/aboveground storage systems could be used as well. But the prices get large...
Its a tough issue, without a simple or single solution.