As stormwater regulations become increasingly stringent for hydrologic and water quality control, Department of Defense (DoD) facilities are faced with the daunting task of simultaneously complying with multiple laws and regulations, such as the Energy Independence and Security Act (EISA) of 2007, Clean Water Act Total Maximum Daily Loads (TMDLs), and Municipal Separate Storm Sewer Systems (MS4) permits. This oftentimes requires facilities to plan, design, and implement structural best management practices (BMPs) to capture, filter, and/or infiltrate runoff. These requirements can be complicated, contradictory, and difficult to plan for. As a result, many DoD facilities over-build or over-size these BMPs to ensure compliance.

This project demonstrated a Stormwater Management Optimization Toolbox (SMOT) that was specifically designed to help DoD facilities achieve compliance with regulatory stormwater requirements for the minimum cost possible. The demonstration took place in two phases: (1) demonstrate that the Model Selection Tool (MST) recommendation accurately results in the minimum BMP cost for 45 facilities of widely varying climatic and regional conditions, and (2) demonstrate SMOT at two facilities to showcase the capabilities of the model platforms, illustrate the ease of implementation, and ultimately validate the model selection element.

This project will demonstrate a Stormwater Management Optimization Toolbox that is specifically designed to help DoD facilities achieve compliance with regulatory stormwater requirements for the minimum cost possible. The toolbox identifies the most cost-effective modeling method based on a facility’s local conditions, provides a range of modeling platform sophistication, and facilitates ease of implementation. The demonstration will take place in two phases:

1. Validate that the modeling method recommendation accurately results in the minimum BMP cost for 45 facilities of widely varying climatic and regional conditions.
2. Demonstrate the toolbox at two facilities to showcase the capabilities of the model platforms, illustrate the ease of implementation, and ultimately validate the model selection element.

SMOT is a spreadsheet based tool comprised of the MST, Scaled Model Platforms, and BMP Sizing Tool/Master Plan. SMOT has the ability to effectively analyze and plan for BMP implementation, resulting in potential cost savings by reducing BMP sizes while simultaneously achieving compliance with multiple objectives. SMOT identifies the most cost-effective modeling method based on an installation’s local conditions (soils, rainfall patterns, drainage network, and regulatory requirements).

Using national data sets, SMOT receives watershed characteristics information and processes the information through the MST, which makes recommendations of the modeling method to use. SMOT recommends one modeling method out of three possible alternatives: a simple design storm approach (e.g. the 95th percentile rainfall treatment), a simple continuous simulation approach, or a continuous simulation approach that is coupled with optimization. After the general modeling method is identified by the MST, specific watershed models identified in the Scaled Modeling Platforms are utilized to carry out the modeling analysis. Modeling results from the recommended platform are then fed into the BMP Sizing Tool to guide the implementation process. The BMP Sizing Tool within SMOT estimates the required BMP sizes for the new development for the subwatershed in which the new development occurs, the area of the new development, and the desirable type of BMP to be implemented. On the basis of the modeling results, the BMP Sizing Tool interpolates the BMP volume and area (expressed in the depth of runoff to be captured/infiltrated) required as development occurs in the subwatershed of interest. If development is planned for a subwatershed with constraints identified, SMOT helps select a substitute location (subwatershed) within the larger watershed with higher potential infiltration than the proposed development subwatershed. The BMP Sizing Tool allows a design engineer to select the type of BMP, size the BMP, and customize layer depths of a BMP. Finally, SMOT provides a basic report of the selected BMP including typical cross-section of the BMP and major dimensions.

SMOT is able to assist with stormwater management efforts varying from analysis method selection (MST), actual modeling analysis (Scaled Modeling Platforms), to final BMP implementation (BMP Sizing Tool or BMP Master Plan) across DoD facilities. The Toolbox is expected to help DoD facilities achieve substantial cost savings during the process of complying with stormwater regulations.

For Phase 1 the project team effectively demonstrated the MST at 45 installations across varying climatic and regional conditions. MST was able to match runoff predictions by the stormwater Management Model (SWMM) with a strong correlation of R2>0.98 and a low relative absolute error for total runoff volume (RAE<10%). When MST was assessed against the System for Urban Stormwater Treatment Analysis and Integration (SUSTAIN) overflow, MST was able to mimic outputs with a high level of correlation (R2>0.99) and close approximation in total runoff volume (RAE<10%). It was concluded that the MST could serve as a reasonable alternative to the SWMM for runoff volume and SUSTAIN model for BMP simulations. 

In Phase 2 the project team successfully demonstrated SMOT at two facilities, Aberdeen Proving Grounds (APG) and Naval Air Station (NAS) Key West. The team conducted a full-scale demonstration using detailed modelling approaches for continuous simulation coupled with or without optimization (SWMM or SUSTAIN). These modeling approaches were applied for a single subwatershed at each installation and then at the subcatchment basin for NAS Key West. The selected subwatersheds within each installation had development potential, so modeling was conducted for 30%, 60%, and 90% impervious surface. BMP size results from the full-scale modeling efforts were compared against each of the modeling approaches and finally the original MST recommendations and SMOT outputs. For APG, the BMP size results from the full-scale modeling efforts resulted in outputs within 10% of each other and greater than the continuous approach by 10% for the Design Storm approach. These results confirm that optimization does not yield significant savings for APG and that the recommendations from MST and detailed modeling efforts are consistent at APG. 

Full scale modeling at NAS Key West identified that continuous simulation coupled with and without optimization resulted in BMP sizes that were 10% smaller in size than the continuous simulation. When models were applied at the subcatchment scale, the resulting BMP sizes again confirmed that the continuous simulation with optimization was the correct modeling approach for NAS Key West. These results validated the MST outputs and confirmed that the MST is appropriate and applicable at all scales.

The use of SMOT has the potential to help DoD identify appropriate modeling approaches and significantly reduce BMP implementation costs. SMOT helps eliminate the guesswork of selecting a model method, it can reduce modeling costs by predicting when sophisticated modeling can be avoided, help reduce BMP sizes and costs through optimization when it is cost-effective, and finally can streamline the compliance and design processes by providing simplified guidance in the form of a BMP Sizing Tool or Master Plan.