**4.3 BMPs and other protections**

For non-point source control, the construction of some type of infrastructure is required due to the diffuse nature of the pollutant. This field has taken on a wide variety of terms [63]. Low Impact Development (LID) is construction that attempts to mimic the natural hydrology and so encompasses any installation that reduces stormwater impact. Water Sensitive Urban Design (WSUD) is a similar approach and includes any effort to minimize the hydrological impacts of urban development on the surrounding environment. Integrated urban water management (IUWM) is a somewhat broader concept combining the management of water supply, groundwater, wastewater and stormwater. Sustainable Urban

Drainage Systems (SUDS) consist of a range of technologies and techniques used to drain stormwater/surface water in a manner that is (arguably) more sustainable than conventional solutions. Best Management Practices (BMPs) are those practices that possess both non-structural (street sweeping) and structural (retention pond) attributes that minimize impact of stormwater. Stormwater Control Measures (SCMs) are identical but this term is used to eliminate the idea of best because alternative practices (not the best ones) can be used. Alternative techniques (ATs) or compensatory techniques (CTs) describe structures used to reduce runoff volume, peak flows and flooding. Some of these techniques can be considered for the protection of the quality of receiving environments. Source Control (SC) is used for on-site stormwater systems. Green Infrastructure (GI) is the part of urban planning that utilizes green space hubs and corridors highlighting their potential ecosystem services.

All technologies are designed to provide benefits to the urban environment and to mitigate the harmful effects of stormwater. The effectiveness of these technologies is dependent on soil characteristics, proper design and installation. Many may be limited by the volume of water flowing into them as retention time is a critical component for effective treatment. Soil is another critical component. A soil with a slow percolation rate cannot handle the volume of water that a good percolating soil is able to infiltrate. The percolation of soil must also be considered in flooding risk. As soil moisture exceeds 45%, pervious areas generate runoff contributing directly to stream discharge. Thus, green infrastructure is now understood to underperform in large and high intensity storm events resulting in flooding [64].

Retention or detention basins and small ponds are the most common technologies installed due to cost and ease of construction. These basins meet multiple design criteria from peak shaving that is required for any land disturbing activity to infiltration by pooling water allowing it to infiltrate. Retention basis (ponds) also provide habitat and recreational opportunities making them appealing in communities. These ponds (<0.01 Km<sup>2</sup> ) may be responsible for 34% of the nitrogen, 69% of the phosphorus and 12% of the sediment masses retained collectively by all aquatic components in the watershed [65]. More study is needed to quantify the collective impact the network of these small ponds has on urban watersheds.

We now have an ability to create a water sensitive city [66]. This includes the ubiquitous use of plants in any design to create the potential for removal nutrients and other pollutants. Green roofs installed on rooftops now intercept precipitation reliving some of the burden on the stormwater infrastructure and the need for peak attenuation. Building blue roofs to create water storage keeps water out of the stormwater cycle easing the burden on stormwater infrastructure. These alternatives provide a visual improvement over a conventional roof top and a return on investment by lowering environmental costs. They also help to regulate building temperatures improving energy efficiencies. Green design forces water discharge from roads into some form of bioretention further improving water quality [67, 68]. With these designs, stormwater is still flowing but at a reduced rate and with better quality.

Wetlands with or without larger impoundments add water quality treatment, support a diversity of wildlife and provide recreational opportunities within urban environments. The key component of these designs is retention of water in the system. Entering water is spread out evenly and soils constantly inundated to produce the reduced water conditions needed for a wetland. Wetlands can improve stormwater considerably by absorbing flow and mitigating concentrations of nutrients and bacteria [69]. Recreational boardwalks and interpretation signage are additional features these environments provide.
