Perez-Pedini et al 2005

Perez-Pedini C, Limbrunner JF, Vogel RM (2005) “Optimal location of infiltration-based best management practices for storm water management,” JOURNAL OF WATER RESOURCES PLANNING AND MANAGEMENT, 131(6) pp. 441-448

This article examined a methodology for locating the optimal placement of infiltration-based stormwater BMPs. The goal was to reduce the peak runoff flow based on implementing a budget of 25 to 400 BMPs (the results would be a pareto frontier with the number of BMPs implemented on one axis and the percent reduction of peak flow on the other axis).

The researchers modeled a developed watershed as a grid made up of 4,533 hydrologic response units (HRUs) which could be modeled as having a BMP implemented or not. If it was decided to implement a BMP in an HRU, then the CN of the HRU would be decreased by 5 units. The researchers planned to run a genetic algorithm to decide where to place the BMPs. However, testing 4,533 HRUs for possible BMP implementation was too large of a decision space for a GA to handle, and the researchers had to make some limitations to reduce this decision space. They made the decision to limit possible BMPs to HRUs with low permeability (high CN) and HRUs which were in close proximity to a river. The first limitation makes sense that the most effective BMP would be removing an impervious surface, and the second limitation of being close to a river makes sense because it will likely have a larger volume of water running over it than an HRU at a high point in the watershed.

The results of the study find that the first few BMPs implemented have a high reduction in peak flow per BMP, and as the number of BMPs implemented increases, the reduction in peak flow per BMP decreases. This makes sense as the GA should automatically target the very best locations first and then the less effective HRU locations for BMPs will get selected.

I was surprised that the article mentioned that the GA didn't find the optimal solution, as discovered when they played around with the results a little. If they say their results are acceptable because they are near-optimal, I'll believe them, but I would've liked to see this proven a little more in the paper. Perhaps that is for another paper. Another component I would've liked to see expanded on was their study of possible commonalities between selected HRUs. They concluded that there were no dominating characteristics which could identify good HRUs without use of the GA, and I would be interested to read an article which examined this in detail. I suppose since they found no dominating characteristics, the article results might not be interesting enough to warrant an article.