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Stormwater Management 3427 Miguelito Court, San Luis Obispo, CA 93401 Phone: 805.541.4509 Fax: 805.546.0525 Email: [email protected] WWW.OASISASSOC.COM Stormwater Management HYDROMODIFICATION AND LOW IMPACT DEVELOPMENT Due to the recent development of large, costly end-of-pipe facilities new hydromodifi cation criteria located at the bottom of drainage The California State Water by both the California State Wa- areas, LID addresses stormwater Resources Control Board ter Resources Control Board and through small, cost-effective land- and the Central Coast the Central Coast Regional Wa- scape features located at the lot RWQCB have developed new hydromodifi cation criteria that ter Quality Control Board, new level. will require effective stormwater development and redevelopment management practices. projects will have to be cogni- These landscape features, known zant of implementing stormwater as Integrated Management Practic- management practices into their es (“IMPs”), are the building blocks design. Stormwater management of LID. Almost all components of is the mechanism for controlling the urban environment have the stormwater runoff in order to re- potential to serve as an IMP. This duce downstream erosion, reduce includes not only open space, but water quality degradation, prevent also rooftops, streetscapes, park- fl ooding, and mitigate any adverse ing lots, sidewalks, and medians. effects on the aquatic environment LID is a versatile approach that caused by changes in land use. Low can be applied equally well to new Impact Design (“LID”) is an inno- development, urban retrofi ts, and vative and comprehensive storm- redevelopment / revitalization water management approach with projects. This bioswale, located in San Luis a basic principle that is modeled Obispo, was constructed in 2005. Bio- after nature: manage rainfall at swales are an excellent method of Low Impact Design. the source using uniformly dis- tributed decentralized micro-scale controls. The Central Coast Regional LID’s goal is to mimic a site’s Water Quality Control predevelopment hydrology by us- Board “RWQCB” (Region ing design techniques that infi l- 3) extends from Santa Cruz trate, fi lter, store, evaporate, and County to Santa Barbara County. detain runoff close to its source. Techniques are based on the prem- ise that stormwater management should not be seen as stormwater disposal. Instead of conveying and managing / treating stormwater in STORMWATER MANAGEMENT, CONT... PAGE 2 Why Low Impact Design? Regulatory Compliance option to pursue the Joint Effort. The California State Water Re- Following the initial project scop- sources Control Board (“State ing, the Central Coast’s RWQCB’s Board”) has been working to de- “Joint Effort” will consist of two velop a statewide hydromodifi ca- (2) phases – the fi rst will focus on tion control methodology and asso- initial implementation and refi ne- ciated criteria, policy, and permit ment of the methodology (for de- requirements. Similarly, the Cen- velopment of hydromodifi cation tral Coast Regional Water Qual- control criteria), while the second ity Control Board (“RWQCB”) (lo- will focus on further implement- cated in Region 3) has developed ing the methodology that is estab- a multi-phase, multi-year “Joint lished. The overall project goal is to Effort for Hydromodifi cation Con- develop an approach to the man- trol” (“Joint Effort”) that allows agement of hydromodifi cation that participating municipalities to aid will meet both resource protection This bioswale, located at Avila Sea- / adhere to the development of goals and regulatory requirements. side Lodge, was constructed in 2005. specifi c hydromodifi cation control Bioswales are an excellent method of criteria that follow specifi cally out- The hydromodifi cation criteria de- Low Impact Design. lined Best Management Practices veloped by both the State Board (“BMPs”). This effort is being lead and the Central Coast RWQCB will Environmental and Economic by the Central Coast Low Impact make LID a regulatory requirement Sustainability Development Center. The work for new development and redevel- completed by the Central Coast opment projects. Thus, it is in the Low Impact Design (“LID”) has RWQCB intentionally overlaps and best interest of those involved in numerous benefi ts and advantag- coordinates with the State Board’s these projects to implement inte- es over conventional stormwater work and will assist other Regional grated management practices into management approaches. In short, Boards and the State Board in di- the design to achieve full regula- it is a more environmentally sound recting municipalities in how to tory compliance. technology and a more economical- successfully develop scientifi cally ly sustainable approach to address- sound and understandable hydro- ing the adverse impacts of urban- modifi cation criteria. ization. By managing runoff close to its source though intelligent site It should be noted that California design, LID can enhance the local law requires operators of certain environment, protect public health, municipal separate storm sewer and improve community livability - systems (MS4s) to develop and im- all while saving developers and lo- plement storm water management cal governments money. plans that will reduce pollutant loadings to the maximum extent practicable, and must investigate and eliminate illicit connections Low Impact Design is an to the storm sewer system. MS4s The Central Coast RWQCB would like environmentally sound are divided into three general cat- to work with different municipalities technology that addresses egories based on size criteria – the to develop and implement stormwa- the adverse impact of ter management plans. Image from “small MS4s” have been given the www.architecture.uark. urbanization. STORMWATER MANAGEMENT, CONT... PAGE 3 Specifi c Integrated Management Practices: It is important to understand how well drained, infi ltration can also be The “swale” component of the to manage the initial surface runoff facilitated in the swale by placing bioswale provides pre-treatment of a rainstorm (i.e., “fi rst fl ush”). ditch blocks or weirs perpendicu- of stormwater to remove coarse During fi rst fl ush, rapid changes in lar to the fl ow path, causing small to medium sediments, while the water quality can occur due to pol- volumes of water to be captured in bioretention system removes fi ner lutants deposited in exposed areas the swale and allowing more time particulates and associated con- becoming dislodged and entrained for infi ltration. taminants. Bioswales are able to by the rainfall-runoff process. Usu- fi lter stormwater via the following ally the stormwater that initially processes: runs off an area will be more pol- luted than the stormwater that • Passing through surface veg- runs off later, after the rainfall has etation; ‘cleansed’ the catchment. • Percolating through prescribed fi lter media (which provides The existence of the fi rst fl ush of treatment through fi ne fi ltra- pollutants provides an opportunity tion, extended detention treat- for controlling stormwater pollu- ment, and some biological up- tion from a broad range of tech- take); niques. First fl ush collection sys- • Disconnecting impervious ar- tems are employed to capture and eas from downstream water- isolate this most polluted runoff, ways; and with subsequent runoff being di- • Providing protection to natural verted directly to the stormwater hydraulic systems from storm This bioswale, located at Tompkins system. The following integrated Medical Plaza, was constructed in events by reducing storm fl ow management practices have proved 2006. velocities when compared to to be effective in managing fi rst pipe systems. fl ush. Bioswales A biowale is a form of bioretention used to partially treat water quality, attenuate fl ooding potential, and convey stormwater away from crit- ical infrastructure. These systems are linear, and are often used as an alternative to, or enhancement of, traditional stormwater piping. Bioswales are often integrated into parking lot and road medians and parallel to roadways to infi ltrate and treat a portion of the stormwa- The overall design of a bioswale will vary depending upon its location, its ter volume. These systems can of- desired outcome, etc. The cross section above depicts the general design of a ten be integrated into existing ditch bioswale with an underdrain. Surface runoff from the adjacent impervious area enters the swale through a gravel strip and then fl ows through vegetative and swale systems to increase their buffers along the edge of the bioswale. Image from UF IFAS Extention Bioswale treatment function. Where soils are Fact Sheet. STORMWATER MANAGEMENT, CONT... PAGE 4 Specifi c Integrated Management Practices: Rain Gardens scape scheme, which can increase the quality of life in urban areas by Rain Gardens collect, absorb, and adding beauty, habitat value, and fi lter stormwater runoff from roof reducing urban heat island effects. tops, driveways, patios, and other areas that are not permeable. They The system consists of a container are shallow depressions that can be fi lled with a soil mixture, a mulch a variety of shapes and sizes and can layer, under-drain system and a utilize a variety of different plants. shrub or tree. Stormwater runoff All rain gardens are constructed drains directly from impervious with soil mixes that allow water to surfaces through a fi lter media. soak in rapidly and support healthy Treated water fl ows out of the sys- plant growth. Specifi c benefi ts may tem through an under drain con- include: The deep-rooted plants, permeable nected to a storm drainpipe / inlet soil, depth, and overall location of or into the surrounding soil. Tree any given rain garden aid in the col- • Filtration of oil, grease, pesti- lection, absorbsion, and fi ltration of box fi lters can also be used to con- cides, etc. from driveways and stormwater runoff. trol runoff volumes / fl ows by add- lawns before they reach storm Image from www.thecoves.ca.. ing storage volume beneath the drains that lead to streams, fi lter box with an outlet control de- wetlands, lakes, and marine Tree-in-a-Box vice.
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