If we consider the opportunities to store runoff on residential sites, and commercial properties, and in residential street right-of-way (the City of Seattle has a program developing prototypes for this), we can do a lot of detention. Maybe enough to help salmon and other fish thrive in this urban creek. Of course, there are also water quality issues to address in order for that to happen. But if we can reduce the number and size of urban floods, we can give the fish a fighting chance.

We developed a spreadsheet that shows how much water could be detained at the watershed scale, depending on what percentage of landowners adopt these detention strategies.  Our "high" estimate used the maximum amount of storage any student managed to accomplish, and our "low" estimate was based on the minimum amount of storage any student in our course accomplished.  We invite you to take a look at this spreadsheet, and imagine what Seattle could be like in 50 years if we started promoting these ideas seriously today.

Excel spreadsheet.(as a Zip file)

The speadsheet looks like this (below). Using a particular set of assumptions about how many parcels begin to implement detention strategies, we can estimate the impact this might have on the detention capacity of the watershed as a whole -- and its ability to function more like a pre-urbanizeation Pacific Northwest landscape.