Nevertheless, a checklist can help focus efforts on the most important runoff channels, and on the most effective methods.
Method's effectiveness------->1 2 2 2 6
Runoff channels Vol filter fence sock grdam basin
Madison St 4 1 x 0 2 0
Adams St 1 1 x 0 2 0
SWend Edgew 1 1 x 0 3 0
NW Terrace Edgew 0 x 3,0 x x 0
Explanation of table
"Vol" = an estimate of the relative volume of runoff from various streets or terraces. The "4" next to Madison Street means roughly 4 times the runoff goes down this street, compared to any other exit path. A "0"was given to runoff from the NW terrace of Edgewood Av, since water is absorbed by the turf and runoff will occur here only during a severe, prolonged strorm.
"Filter" = the cloth filter bags placed into the stormwater inlets. I do not consider these to be very effective.
"Fence" = a cloth fence. These are installed only over soil, so an "x" appears for the streets--the fence can be used only on the terrace. Can be very effective. There are two fences now, hence two numbers. The newer fence seems ineffective.
"Sock" = a silt sock. Can be very effective for small flows.
"Grdam"=gravel dam. The effectiveness of these can vary widely, depending on amount of gravel, gravel size, and whether there is pavement or soil below.
"Basin"=infiltration basin, retention basin, large rain garden, or terrace rain garden. These are the most effective by far, because they retain all sediment, recharge groundwater, and filter pollutants.
I did not include "street sweeping" in the table to keep it small, but obviously, this is the most basic and important technique. We will assume sweeping is employed to the max.
Observed effectiveness ratings (during a storm) for each cell in the table:x=this method is not possible here.
0=This method was not deployed here, or was completely ineffective.
My "observed effectiveness" ratings in the above table are guestimates. I did observe the site during the heavy storm of 5/26, but changes to the perimeter controls have been made since then.
The next step--a spreadsheet for "weighted effectiveness"
The above "raw" table, as is, can be useful as an overview of progress.
The table can be made still more effective if it is "weigthted" for both the relative volume of flow (left column), and the "relative effectiveness" of the method (top row). In other words, you would multiply the score in the above table by both the relative volume and the relative effectiveness. Hence, by this reasoning, a retention basin on Madison Street would be by far the most effective method you could employ for the entire project.
The practicality of such a basin in another matter--but I've made a proposal here. Another possibility would be to use the low ground on the nearby Edgewood College lawn.
The effectiveness of a basin would depend on its size. If large enough, it would have an effectiveness rating of 3. This would give a retention basin serving Madison St. a score of 3 (observed effectiveness) x 4 (relative flow) x 6 (method effectiveness).
A weighted table would provide feedback for everyone involved to see the effectiveness of their efforts.
Conclusions from spreadsheet, as of 6/2/10
- More efforts need to be directed towards Madison Street, the principal runoff pathway.
- Basins would greatly improve the score for this project.
Cloth dams can be very effective, but they must be built on soil. This one near Lake Wingra was left from another project. It sagged and nearly failed here, illustrating that these must be maintained.