X.K. Runoff Capture and Control Requirements
- The purpose of these requirements is to reduce flooding in GHI, reduce negative effects on the Cooperative’s streams, build resiliency, and maintain the Cooperative as a desirable place to live.
- Additional development increases the speed and amount of stormwater runoff and, therefore, increases erosion. The additional runoff can overload the capacity of streams and storm drains.
- Additions, covered patios and decks, sheds, etc. are impervious and prevent or substantially impede the natural infiltration of water into the underlying soil.
- The construction or installation of a roofed structure (e.g., addition, covered patio or deck, sheds, etc.) will require the construction or installation of a runoff capture and/or control measure to offset the additional runoff generated by the structure.
- Several measures are available to Members to capture and/or control any increased runoff resulting from the construction of an exterior alteration, improvement, or addition. These measures are described in more detail below.
- The measures described below also provide guidelines for Members who wish to install one of these measures to better control runoff in their yard unrelated to the construction of an exterior alteration, improvement, or addition.
- Any dimensions included in the example measures presented below are for illustration purposes only and are not pre-approved design dimensions. Each measure proposed for construction must be designed specifically for the Member’s yard.
- The construction or installation of any of the capture and/or control measures described in Sections 6-8 below that are unrelated to the construction of an exterior alteration, improvement, or addition. shall require a Type II permit. Permits are discussed in Section X.C of this Handbook.
- If the construction or installation of any of the capture and/or control measures described in Sections 6-8 below are proposed as part of a proposed exterior alteration, improvement, or addition, the permit application for these measures shall be included as part of the permit application for the proposed exterior alteration, improvement, or addition as described in Section X.C of this Handbook.
- Raingardens
- Raingardens capture and retain runoff and allow the runoff water to infiltrate into the ground.
- Raingardens are planted with water-tolerant plants because the raingarden will remain wet until the runoff water has completely infiltrated into the ground.
- Raingardens should be constructed at least five feet away from the foundation of the unit or row of units.
- An example of a raingarden is shown in Figure 1 below. Design information can be found on the PG County Rain Check website https://cbtrust.org/grants/prince-georges-county-rain-check-rebate/.
Source: City of Portland 2020 Stormwater Management Manual, December 2020, Figure SW-150
Figure 1. Raingarden Cross-Section - Dry Wells
- Dry wells capture and retain roof runoff to allow the runoff water to infiltrate into the ground.
- Dry wells. should be constructed at least 10 to 12 feet away from the foundation of the unit or row of units.
- An example of a dry well is shown in Figure 2 below.
- Rainbarrels
- Rainbarrels and cisterns are another means of capturing runoff to store for later use.
- This later use should be as part of a slow, measured outflow to minimize any negative effects of releasing the water.
- Requirements for rainbarrels and cisterns are contained in Section XXIII of this Handbook.
Source: City of Portland 2020 Stormwater Management Manual, December 2020, Figure SW-110
Figure 2. Dry Well Cross-Section
