FUTURE ENVIRONMENT AND STORMWATER | CHAPTER 12


City or a third party. The City can own and manage BMPs as part of its stormwater facilities and utility. Private parties can own the land with the City holding a util- ity easement and managing the BMPs. Cedar Falls should choose an approach that meets its traditions, needs, staff, and budget.


The TMDL for Dry Run Creek identifies a goal of <10% connected impervious sur- face (CIS). This goal is met easily in new developments with the proper BMPs, so the key is to plan and design with a 10% CIS threshold in mind. The idea behind reducing CIS is to increase residence time, which reduces runoff volume by extend- ing infiltration duration. Groundwater recharge increases stream base flow, reduc- es stream bounce, and dissipates velocities that cause bed and bank erosion. Also, both infiltration and vegetation capture sediment, thereby reducing loads further.


New development BMPs should be integrated with existing stormwater infrastruc- ture. The design must ensure that new BMPs and existing systems work effectively together, with minimal maintenance. Evaluation of stormwater management sys- tems for new developments should be performance-based, not prescriptive. Perfor- mance measures include total runoff volume from a development, discharge rate at storm sewer outfalls, and water quality thresholds for sediment, bacteria, and nu- trients. These performance criteria should be put in place for all new developments in order to have a sustainable stormwater management system which protects and improves the City’s streams and other downstream receiving waters (e.g., Cedar Riv- er). Headwater areas are especially important because stormwater BMPs in these locations benefit all downstream reaches.


EXISTING DEVELOPMENT


Redevelopment and infill projects present a unique opportunity to improve storm- water management in existing developed areas. The TMDL for Dry Run Creek iden- tifies a goal of <10% CIS. However, existing facilities and impervious surfaces in the City make it a challenge to achieve less than 10% CIS in the already-developed sub- watersheds of Dry Run Creek.


Redevelopment and infill projects often lend themselves to hybrid solutions. These encompass both naturalized elements of stormwater treatment trains and also more engineered components. A “Green Street” is an example of a hybrid solution that provides landscaping while managing runoff more effectively than conven- tional designs for a similar area. Green roofs, cisterns, and permeable pavements are other BMPs that can be applied in existing urban areas, dense suburban de- velopments, and many retrofit projects. Where there is enough room (e.g. - malls, corporate facilities, institutions, and in large parking lots), naturalized BMPs may consist of curb cuts that direct runoff to infiltration swales and basins, and even treatment wetlands. The most important thing in redevelopment and infill projects is to look for places to slow and hold stormwater runoff, thus promoting infiltration and evapotranspiration. This approach will gradually improve the quality of Dry Run Creek and other streams in Cedar Falls.


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