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--- green_infrastructure [2023/11/16 10:16] – admin
+++ green_infrastructure [2024/05/07 15:04] (current) – admin
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 ====== Green Infrastructure ======
-Green infrastructure is any stormwater practice that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters. Practices that meet this requirement include, but are not limited to, the following: [[rain garden]], [[bioretention device]], [[infiltration basin]], [[grassed swale]], [[permeable pavement]], [[green roof]], planter connected to roof drainage, rain barrel and rainwater harvesting/reuse.
+Green infrastructure is any stormwater practice that use plant or soil systems, permeable pavement or other permeable surfaces or substrates, stormwater harvest and reuse, or landscaping to store, infiltrate, or evapotranspirate stormwater and reduce flows to sewer systems or to surface waters. Practices that meet this requirement include, but are not limited to, the following: [[rain garden]], [[bioretention device]], [[infiltration basin]], [[vegetated swale]], [[permeable pavement]], [[green roof]], planter connected to roof drainage, rain barrel and rainwater harvesting/reuse.
-Dane County requires that for redevelopment with proposed impervious surface area greater than 80% of existing, the first 0.5 inches of runoff from impervious surfaces must be captured using green infrastructure.
+Dane County requires that for redevelopment with proposed impervious surface area greater than 80% of existing, the first 0.5 inches of runoff from impervious surfaces must be captured using green infrastructure. Surfaces designed to generate no runoff from a 0.5 rainfall and are approved by the local approval authority may be considered pervious when determining if this requirement applies to the site.
 =====Modeling Guidance=====
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 **2. HydroCAD**
-Using TR-55, a 0.7-inch rainfall produces 0.5 inches of runoff from an impervious surface (CN=98), as seen in Figure 1. To show that the green infrastructure is able to capture this runoff, a 0.7-inch 24-hour MSE4 design storm (Figure 2) must be modeled with no surface discharges from the practice (Figure 3). Due to the slow rate at which water flows through engineered soil, underground storage should not be incorporated into the model.
+Using TR-55, a 0.7-inch rainfall produces 0.5 inches of runoff from an impervious surface (CN=98), as seen in Figure 1. To show that the green infrastructure is able to capture this runoff, a 0.7-inch 24-hour MSE4 design storm (Figure 2) must be modeled with no surface discharges from the practice (Figure 3). For the most common green infrastructure practices, such as bioretention and permeable pavement, this means all captured water must leave via the underdrain and/or by infiltrating into the native soils. For practices using engineered soil, underground storage should not be incorporated into the model, because of the relatively slow rate at which water flows through the soil.
 [{{ :wiki:images:hydrocad_0.7_to_0.5.png?200 |Figure 1: 0.7-inch rainfall to 0.5 inches of runoff}}]