Mendota watershed - an urban and rural solution

The Lake Mendota watershed has, functionally, two watersheds: urban and rural. My neighborhood is on the urban watershed, and a closer investigation shows that the runoff from my house, sidewalks, and streets flows into the lake via a storm sewer network of pipes leading to an outlet on the shores of James Madison Park. All the issues associated with urban watersheds, such as flashy hydrology, salt and oil pollution, and phosphorus inputs from grass clippings and leaves, are directly linked to the lake via these storm pipes. When you think about it, these pipes are an expressway for surface pollutants to flow unabated into a natural ecosystem. 

The system of storm sewer pipes that comprises my little urban "watershed"

While there are issues with my small urban “watershed”, I wonder how much can be done to remedy these issues? My conclusion: not much. We can’t simply get rid of these storm pipes; there are streets and houses and people living here, and we have to move water somehow! Perhaps we could install a retention pond near the outlet in James Madison Park similar to this one by the Arboretum, but this would likely be expensive and would use up valuable urban park space. Perhaps the only way to reduce the impacts of the urban runoff in my neighborhood is by reducing the harms placed on the watershed itself; reducing leaf litter, the reduction of impervious surfaces where possible, and street sweeping to remove oils would likely be the best option.

A larger question, however, remains. Should we really be focusing on the “urban” Mendota watershed when the “rural” watershed is the main contributor to the loading of Phosphorus to the lake system? Would any reduction in my urban neighborhood be worthless when nothing is done about rural pollutants like nutrient loading, sedimentation, or agricultural pesticides and herbicides? This is up to some debate, but I believe that in order to truly impact the lake, we cannot view the Mendota watershed as “urban” or “rural” but rather as one complete system. Call it something cheesy like the "One Mendota" viewpoint, where the concerns for the lake transcend municipal or political lines. We should find opportunities to reduce the pollutants that we know are impacting water quality, wherever they may be. 

But due to the inherent limited nature of what these opportunities are, we should be wise about how we spend our public dollars and efforts on these reductions. For example, while leaf litter is not the largest contributor of phosphorus loading to the lake, it potentially may have the largest return on investment (ROI) or “bang for your buck”, where a dollar spent on reducing leaf inputs will have the greatest impact on P loading. Therefore, in our “One Mendota” watershed idea, we should begin to identify the projects and locations that would have the most economical ROI, regardless of it’s a rural or urban solution. 

Map of the Mendota Watershed, with the two major land uses of Urban (in red) and rural/agricultural (in orange) visible.

 Map from:  Motew, Melissa & Booth, Eric & Carpenter, Stephen & Chen, Xi & Kucharik, Christopher. (2018). The synergistic effect of manure supply and extreme precipitation on surface water quality. Environmental Research Letters. 13. 10.1088/1748-9326/aaade6.