Assessments of required stormwater management system capacity
The general circulation models (GCM's) used to study climate change consistently predict more intense storms for most regions of the world. Even areas that will receive less total precipitation will see the precipitation that does occur coming in more intense storms. More intense precipitation will result in drainage systems being overwhelmed more frequently.
In order to prepare communities for more intense storms, we reverse-engineer existing drainage systems to establish the present capacity of these systems, and specify capacities required to convey expected peak flows from climate change.
Sample project: For Keene, New Hampshire, we assessed mid-century stormwater management needs by modeling the impacts of both climate change and population growth on the current system. Major analyses:
• Reverse-engineer a sample of existing culverts to establish present capacities;
• Statistically model historical rainfall for the region and apply results of the latest climate change research to predict future rainfall intensity (23% increase over historical design storm);
• Combine rainfall/intensity and runoff-rate predictions to establish peak flow at each culvert;
• Determine the percentage of undersized culverts (44%);
• Design required culvert upgrades and estimate the cost of upgrading the system ($230,000);
• Develop an adaptation strategy that combines methods to reduce peak flow (SUD, BMP), with system upgrades, and prioritize upgrades by risk.
