Chapter 4 - portal.ct.gov · Chapter 4 Site Planning and Design 4.1 Introduction ... 4.4.5 Vegetated Roof Covers.....4-17 Volume 1:Background 2004 Connecticut Stormwater Quality Manual

Chapter 4Site Planning and Design

Chapter 4 Site Planning and Design

4.1 Introduction...................................................................................................4-2

4.2 Site Planning and Design Concepts..........................................................4-2

4.3 Alternative Site Design................................................................................4-4

4.3.1 Streets and Parking Lots .........................................................4-6

4.3.2 Lot Development ....................................................................4-11

4.4 Low Impact Development Management Practices.............................4-13

4.4.1 Vegetated Swales, Buffers, and Filter Strips ......................4-13

4.4.2 Bioretention/Rain Gardens ..................................................4-13

4.4.3 Dry Wells/Leaching Trenches...............................................4-15

4.4.4 Rainwater Harvesting............................................................4-15

4.4.5 Vegetated Roof Covers .........................................................4-17

Volume 1: Background

2004 Connecticut Stormwater Quality Manual 4-1

Site planning and design is a complex process involving a variety ofconsiderations such as zoning regulations (e.g. setbacks, Floor Area Ratioallowances, allowable building density, and height restrictions) andimpacts to traffic, wetlands, and the environment. Site planning is under-taken by the developer or project proponent in conjunction with localand/or state review agencies, typically local Planning, Zoning, and InlandWetlands Commissions and, in some instances, the ConnecticutDepartment of Environmental Protection (DEP) or federal agencies such asthe U.S. Army Corps of Engineers. Due to the complexities of site planningand design, the most effective site planning process occurs through a col-laborative effort between developers and the review agencies before andthroughout the review process.

This chapter addresses recommended site planning concepts and prac-tices that can be incorporated into the design of new projects to providewater quality and quantity benefits and reduce the need for or size of struc-tural stormwater controls. This chapter does not address comprehensiveland use planning (master planning, zoning, open space, conservationeasements, etc.) which is beyond the scope of this Manual. However, thesite planning concepts and practices presented in this chapter should beimplemented through existing local land use ordinances and state regula-tions and programs. Local and state review agencies should encourage theimplementation of these practices through the site plan review process. Inmany instances, communities may need to re-evaluate local codes andordinances to effectively promote the use of the practices described in thischapter. These design concepts are encouraged by DEP, as well as by theConnecticut Department of Public Health (DPH) for protection of watersupplies in public drinking water supply watershed areas.

4.2 Site Planning and Design ConceptsThe concepts presented in this section are central to effective site planningand design for stormwater management and environmental resource pro-tection. Each of these concepts is based on the fundamental objective ofpreserving a site’s natural hydrologic conditions. As discussed in ChapterTwo, the hydrologic conditions and pollutant removal functions of a sitecan be altered significantly as a result of development. The traditionalapproach to site drainage has been to remove runoff from the site asquickly and efficiently as possible through the use of storm sewers andstructural stormwater conveyances, and to provide detention facilities tomanage increases in peak flows. This approach severely reduces the natu-ral hydrologic and water quality functions of the site and contributes to theadverse environmental impacts discussed in Chapter Two.

A guiding principle of effective site planning is to preserve pre-devel-opment hydrologic conditions such as:

❍ Runoff volume and rate

❍ Groundwater recharge

❍ Stream baseflow

❍ Runoff water quality

This can be accomplished through a number of techniques that shouldbe integrated into the site planning and design process wherever possible.These techniques are described in the following sections of this chapter. Incollaboration with DEP’s NPS Program, the University of ConnecticutCooperative Extension System’s Nonpoint Education for Municipal Officials(NEMO) Project offers assistance to Connecticut municipalities in imple-

2004 Connecticut Stormwater Quality Manual4-2

4.1 IntroductionCareful site planning at the out-

set of a project is the most

effective approach for prevent-

ing or reducing the potential

adverse impacts from develop-

ment. Site planning is a

preventive measure that

addresses the root causes of

stormwater problems. Effective

site layouts and designs that

preserve natural features as

well as natural hydrologic and

water quality functions can limit

water quality impacts and the

need for costly structural

stormwater controls, thereby

reducing the costs of develop-

ment. Other potential benefits

of effective site planning include

preservation of open space,

enhanced aesthetic and recre-

ational value, reduced

downstream flooding, and

enhanced land values.


menting these site planning and design strategies.(See Additional Information Sources at the end of thischapter or visit http://www.nemo.uconn.edu).

Designing the Development to Fit the TerrainDevelopments that are designed to “fit the terrain” ofthe site require significantly less grading and soil dis-turbance than those that are designed without regardfor the existing topography. Road patterns shouldmatch the landform by placing roadways parallel tocontour lines where possible. In doing so, naturaldrainageways can be constructed along street rights-of-way, thereby reducing the need for storm pipes.Open space development, allowable in many munic-ipalities, can help preserve large natural areas andopen space as well as make it possible to designaround topographical constraints.

Limiting Land Disturbance ActivitiesLand disturbance activities such as clearing and grub-bing, excavation, and grading result in erosion ofexposed soils, increased sediment loadings, as well asincreased volumes of runoff from a site. Limiting theland area disturbed by development can only beaddressed comprehensively at the site planning level(Schueler, 1995). Land disturbance activities should belimited to only those areas absolutely necessary forconstruction purposes, in keeping with the naturalfeatures of the site, and should be clearly delineatedin the field prior to construction. Land disturbanceactivities in proximity to wetlands, watercourses,steep slopes, and other sensitive resource areasshould be avoided, or minimized if they cannot beavoided. Areas outside the disturbed zone shouldretain natural vegetation. This approach is more suc-cessful on larger lots where large areas ofundeveloped land can be preserved. The successfulapplication of this approach is more difficult and lesspractical on small lots in heavily developed areas(NJDEP, 2000).

Reducing or Disconnecting Impervious AreasReducing and disconnecting impervious surfaces areeffective methods for preserving pre-developmenthydrology. Reducing impervious coverage on a sitedirectly limits the adverse impacts associated withimpervious coverage. On a watershed basis, reduc-tions in impervious coverage contribute directly to theecological health of streams and receiving waters, asdescribed in Chapter Two. Impervious surfaces thatare not directly connected to the drainage collectionsystem contribute less runoff and smaller pollutantloads than hydraulically connected impervious sur-faces. Isolating impervious surfaces also promotesinfiltration of stormwater runoff. Specific techniquesfor reducing or disconnecting impervious areas forroad and lot development are described in Section 4.3 Alternative Site Design.

Preserving and Utilizing Natural Drainage SystemsThe goal of traditional drainage design, to collect andconvey stormwater runoff from the site as efficientlyas possible, is in direct conflict with the objectives ofwater quality design, which is to slow down andattenuate runoff to allow filtration, infiltration, biolog-ical uptake, and settling of pollutants. Naturaldrainage features such as vegetated swales and chan-nels and natural micro-pools or depressions shouldbe preserved or incorporated into the design of a siteto take advantage of their ability to infiltrate andattenuate flows and filter pollutants. The use of natu-ral overland drainage features such as stabilizedswales, where soil and hydraulic conditions allow,and the discharge of stormwater in a diffuse mannerfrom level spreaders should be encouraged as analternative to traditional storm sewer systems.Consistent with this approach is to design roads andparking areas at higher elevations in the landscapeand locate existing swales along back lot lines withindrainage easements (Pennsylvania Association ofConservation Districts et al., 1998). Natural low areasor depressions in the landscape should be preservedwhere possible to maintain infiltration of runoff inthese areas similar to pre-development conditions.

Providing Setbacks and Vegetated BuffersSetbacks and vegetated buffers provide protection ofadjacent natural resources from areas of intensivedevelopment. A setback is the regulated area betweenthe development and a protected area such as a wet-land. A vegetated buffer is an area or strip of land ofpermanent undisturbed vegetation adjacent to a waterbody or other resource. Buffers protect resourcesfrom adjacent development during construction andafter development by filtering pollutants in runoff,protecting water quality and temperature, providingwildlife habitat, screening structures and enhancingaesthetics, and providing access for recreation.Characteristics such as width, target vegetation, andallowable uses within buffers are managed to ensurethat the goals designated for the buffer are achieved(Center for Watershed Protection, 1998b). Buffersalong watercourses also serve to function as green-ways that provide for connectivity of open spaceareas, allowing the movement of wildlife and theopportunity for passive recreation. The dual benefitsthat buffers provide for the protection of water qual-ity from stormwater runoff and the creation ofgreenways are extremely important and complemen-tary. Table 4-1 summarizes the benefits that can beachieved by buffer systems.

As a general rule, one hundred feet of undis-turbed upland along a wetland boundary or on eitherside of a watercourse is recommended as a minimumbuffer width depending on the slope and sensitivity ofthe wetland or watercourse. A conceptual three-zone


stream buffer system designed for protecting aquaticresources while providing flexibility for developmentis shown in Figure 4-1 (Center for WatershedProtection, 1998a, adapted from Welsh, 1991). Eachzone can have designated functions, width require-ments, and management requirements.

Minimizing the Creation of Steep SlopesDevelopment or disturbance of steep slopes cre-ates the potential for erosion and significantsediment loadings in the absence of effective sta-bilization measures. Development destroysvegetation, root systems, and soil structure(Pennsylvania Association of Conservation Districtset al., 1998). Although the definition of steepdepends on soil characteristics and erodibility,slopes steeper than 10 percent, or even flatterslopes with highly erodible soils, typically requirestabilization. The area and duration of disturbanceon steep slopes should be minimized. Soil stabi-lization measures should be implemented inaccordance with local erosion and sedimentationcontrol ordinances, as well as the ConnecticutGuidelines for Soil Erosion and Sediment Control(Connecticut Council on Soil and Water Conservationand the Connecticut Department of EnvironmentalProtection, 2002).

Maintaining Pre-Development VegetationPre-development vegetation should be maintained tothe extent possible, especially on streambanks thatmight otherwise be cleared for view enhancement.Vegetation intercepts rainfall and promotes evapo-

transpiration, thereby reducing the volume of runofffrom a site. In addition to providing erosion control,trees also provide shade to minimize thermal impactsto surface waterbodies. Trees and other vegetationcan be incorporated into a site by planting additionalnative vegetation, clustering tree areas, and conserv-ing existing native vegetation. Wherever practical,trees should be incorporated into community openspace, street rights-of-way, parking lot islands, andother landscaped areas.

4.3 Alternative Site DesignA variety of innovative site design practices have beendeveloped as an alternative to traditional developmentto control stormwater pollution and protect the ecolog-ical integrity of developing watersheds. Thesealternative site design practices are based on the con-cepts described in the previous section, such asreducing site imperviousness and disturbed areas, pre-serving natural site features, and promoting infiltrationthrough the use of natural vegetated conveyances.Research has demonstrated that alternative site designcan reduce impervious cover, runoff volume, pollutantloadings, and development costs when compared totraditional development (Center for WatershedProtection, 2000). Table 4-2 summarizes the docu-mented benefits of alternative site design. Several factors have limited the widespread applica-tion of alternative site design principles inConnecticut and other parts of the country.Alternative site design is a relatively new concept, dat-ing back only to the early 1990s, and involvesfundamental changes to development practices that

Source: Adapted from Center for Watershed Protection, 1998a.

Table 4-1 Benefits of Watercourse Buffers

Benefit

Reduce nuisance drainage problems and complaints Prevent disturbance of steeps slopes

Allow for lateral movement of streams Mitigate stream warming

Provide flood control Preserve important terrestrial habitat

Reduce stream bank erosion Supply conservation corridors

Increase property values Maintain essential habitat for amphibians

Enhance pollutant removal Fewer barriers to fish migration

Provide opportunities for Greenways Discourage excessive storm drain enclosures/channel hardening

Provide food and habitat for wildlife Provide space for stormwater treatment practices

Protect associated wetlands Allow for future restoration


are typically dictated by a complex mix of local zon-ing, subdivision, and building ordinances. Typicalconventional development rules are often inflexibleand restrict development options regarding site planparameters. Consumer demand for wide streets, longdriveways, expansive parking lots, and large-lot sub-divisions, whether perceived or actual, has alsolimited the use of alternative site design concepts bythe development community.

This Manual encourages the use of alternativesite design practices to the extent that local devel-opment rules will allow, to achieve the benefitslisted in Table 4-2, as well as to reduce the needfor and size of end-of-pipe stormwater treatment.However, the Manual also recognizes that commu-

nities may need to re-evaluate local codes andordinances to overcome these challenges andeffectively promote the widespread use of alterna-tive site design practices. Recommended sources ofinformation on how communities can modify localdevelopment rules to reduce impervious cover,conserve natural areas, and prevent stormwaterpollution are provided at the end of this chapter.

A unique demonstration project is currentlyunderway in Connecticut to compare the stormwaterrunoff quantity and quality emanating from traditionaland alternative residential development sites. TheJordan Cove Urban Watershed Monitoring Project is apaired-watershed monitoring study funded, in part,through the Connecticut Department of Environmental

Figure 4-1 Typical Three-Zone Urban Buffer System

STREAMSIDEZONE MIDDLE ZONE OUTER ZONE

Fence

PostingBike path

Foot path

Stream

Source: Center for Watershed Protection, 1998a (adapted from Welsh, 1991).

Table 4-2 Benefits of Alternative Site Design

Benefit

Protection of surface water quality A more aesthetically pleasing and naturally attractive landscape

Reduction of stormwater pollutant loads Safer residential streets

Reduction of soil erosion during construction More sensible locations for stormwater facilities

Reduced development construction costs Easier compliance with wetland and other resource protection regulations

Increases in local property values and tax revenues Neighborhood designs that provide a sense of community

More pedestrian friendly neighborhoods Urban wildlife habitat through natural area preservation

More open space for recreation Protection of sensitive forests, wetlands, and habitats

Source: Adapted from Center for Watershed Protection, 1998a.

Terrain Classification1 Level Rolling Hilly

Development Density2 Low Med High Low Med High Low Med High

Right of Way Width (ft) 50 60 60 50 60 60 50 60 60

Pavement Width (ft) 20-24 28 36 20-24 28 36 28 28 36

Sidewalks and Bicycle Paths (ft) 0 4 5 0 4 5 0 4 5


Protection and by the U.S. Environmental ProtectionAgency’s Section 319 National Monitoring Program(NMP). The study is examining differences in runoffquantity and quality from three watersheds located inWaterford, Connecticut, including an existing controlwatershed with traditional residential developmentand a newly constructed residential development splitinto two distinct neighborhoods, one with traditionalsubdivision design and the other with open spacedesign and a variety of Low Impact Developmentpractices. Post-construction flow and water qualitymonitoring will continue for three years after build-out. The results of this are expected to providequantitative, real-world comparisons of the benefitsand challenges of alternative site design.

A number of recommended alternative sitedesign practices are described in the following sec-tions. These practices are loosely organized into twocategories:

❍ Streets and Parking Lots

❍ Lot Development

4.3.1 Streets and Parking LotsThese practices address the design of streets, parkinglots, and other impervious surfaces associated withvehicular traffic in residential and commercial areas.

Reducing Street WidthsMany residential streets are wider than necessary.Reducing the width of streets can reduce impervious

surfaces in a watershed. Other benefits of narrowerstreets include reduced clearing and grading impacts,reduced vehicle speeds (i.e., “traffic calming”), lowermaintenance costs, and enhanced neighborhoodcharacter. Reducing or eliminating on-street parkingcan reduce road surfaces and overall site impervious-ness by 25 to 30 percent (Sykes, 1989). In some areas,curbing can be eliminated to encourage sheet flowand facilitate the use of vegetated roadside swales.Eliminating curbing in residential and rural areas withnearby vernal pool habitat also allows amphibianmigration across roads. An alternative to eliminatingcurbing is the use of Cape Cod curbing, which allowsamphibians to climb.

Residential streets should be designed for theminimum required pavement width needed to sup-port travel lanes, on-street parking, as well asemergency, maintenance, and service vehicle access.Residential street widths should be based on thefollowing four variables:

❍ Traffic Volume: A simple rule of thumb regard-ing traffic volume is the fewer the vehicles, thenarrower the road may be. Many communitiesrequire a minimum width of 32 to 34 feet ofpavement or two, adjacent 16- to 17-foot travellanes for all roads. Research shows that 20-to24-foot road widths (two 10- to 12-foot travellanes) are adequate for most local roads.

Source: Guidelines for Residential Subdivision Street Design, Institute of Transportation Engineers, Washington DC, 1993, in Universityof Connecticut, Transportation Institute, Technology Transfer Center Fact Sheet.1Terrain Classification: Level – grade of 0% to 8%, Rolling – >8% to 15%, Hilly – >15%2Development Density: Low – 2 or fewer dwelling units/acre, Med – >2 to 6 dwelling units/acre, High – more than 6 dwelling units/acre

Table 4-3 Minimum Residential Roadway Width Guidelines


❍ Design Speed: Slower design speeds allow fornarrower road widths. Local residential roadsshould be designed to provide safe access tohomes. Research indicates that as residentialstreets widen, accidents per mile per yearincrease exponentially and that the safest resi-dential street width is 24 feet (Swift et al., 1998).

❍ Lot Width: As a general rule, large lots with longfront yards require less on-street parking sincelarge lots by their very nature have enough area toaccommodate on-site parking. Roads serving largelots do not have to be designed with on-street park-ing lanes and therefore can be narrower.

❍ Parking Needs: The need for on-street parkingis often used to justify wider residential streets.Roads designed to provide overflow parking fromadjacent lots require one or two additional park-ing lanes. However, not all roads are designed toaccommodate on-street parking and therefore donot require additional parking lanes.

(NEMO Technical Paper #9, Roads, Gibbons 1998a):The standard 50- to 60-foot right-of-way width is rec-ommended to provide adequate emergency accessand parking. However, the paved portion of the right-of-way should be minimized to the extent possible.Table 4-3 presents minimum roadway width guide-lines for residential subdivision street design.

Reducing Street Lengths through AlternativeStreet LayoutStreet lengths and, therefore, total site impervious-ness can be reduced through alternative street andsubdivision layouts. Figure 4-2 illustrates how alter-nate layouts can reduce roadway impervioussurfaces by up to 26 percent.

No single street layout is appropriate for all res-idential development. Roadway layout is highlydependent on site topography, density, traffic vol-ume, and overall subdivision design. Residentialareas with low traffic volume and minimal topo-graphical relief have the most flexibility in design. InConnecticut, a majority of residential subdivisionsuse the “loops and lollipops” and “lollipops on astick” configurations. These road layout designs uti-lize cul-de-sacs, loops, and short feed streets toaccommodate the contours and natural features of asite. Open space development, a compact form ofdevelopment that concentrates density on one por-tion of the site in exchange for reduced densityelsewhere, also lends itself to reduced street lengths.Grid-based street layouts tend to have relativelylonger overall street lengths. The exception is tradi-tional neighborhood design, which incorporatescommunity open space, a variety of housing types,and mixed land uses in a single project to emulatethe characteristics of smaller, older communities(Center for Watershed Protection, 1998a).

Figure 4-2 Alternative Street Layout

Source: Prince George’s County, Maryland, 1999 (adapted from ULI, 1980).

Fragmented Warped Loops and LollipopsGridiron Parallel Parallel Lollipops on a Stick

20,800 19,000 16,500 15,300 15,600

Approximate lineal feet of pavement


Alternative Cul-de-sac DesignCul-de-sacs have a large bulb located at the closedend of the street to enable emergency and servicevehicles to turn around without having to back up.Traditional cul-de-sacs utilize a large-radius, pavedturnaround that can dramatically increase the imper-viousness of a residential subdivision. Alternatives tothis traditional design include turnaround bulbs withsmaller radii and the use of a landscaped island (i.e.,rain garden or bioretention area) in the center of thecul-de-sac to collect rainwater from the end of theroadway.

Reducing the radius of a typical cul-de-sac turn-around from 40 to 30 feet can reduce imperviouscoverage by nearly 50 percent (Schueler, 1995). A 30-foot radius will accommodate most vehicles andreduce pavement. Cul-de-sac bioretention islandshave been used successfully in various parts of thecountry, including a demonstration subdivision inWaterford, Connecticut. These islands can be land-scaped with low maintenance perennials or shrubsappropriate for the soil and moisture conditions.Bioretention and rain gardens are discussed later inthis chapter. If a cul-de-sac island is used, the cul-de-sac radius should allow for a minimum 20-foot wideroad. To make turning easier, the pavement at the rearcenter of the island may be wider (MetropolitanCouncil, 2001). Figure 4-3 illustrates these cul-de-sacdesign concepts.

Reducing the Use of Storm SewersThe use of swales and other vegetated open channelsshould be encouraged in residential streets, parkinglots, and back yards in place of conventional stormdrain systems. Open vegetated channels provide thepotential for infiltration and filtering runoff fromimpervious surfaces, as well as groundwater rechargeand reduced runoff volume. In addition to the waterquality benefits that open vegetated channels provide,these systems are also significantly less expensive toconstruct than conventional storm drain systems. Theuse of vegetated drainage swales in lieu of conven-tional storm sewers may be limited by soils, slope,and development density. In many cases, subdivisionordinances discourage or prohibit the use of openvegetated channels for roadside drainage due to con-cerns over inadequate drainage, maintenance issues,pavement stability, and nuisance insects (if water isallowed to stand for longer than 7 to 10 days). Thispractice requires educating local citizens and publicworks officials who expect runoff to disappearquickly after a rainfall event (Pennsylvania Associationof Conservation Districts et al., 1998).

Reducing Parking Lot SizeParking lots are the largest component of imperviouscover in most commercial and industrial land uses(Center for Watershed Protection, 1998a). The number

of parking spaces at a site is determined by local park-ing ratios which dictate the minimum number of spacesper square foot of building, dwelling units, persons, orsimilar measure. Parking ratios are typically set as min-imums, not maximums, thereby allowing for excessparking. In addition, local parking codes often requirestandard parking stall dimensions to accommodatelarger vehicles. A recent parking study conducted forthe Northwestern Connecticut Council of Governmentsand Litchfield Hills Council of Elected Officials demon-strated that, in most cases, demand for parking is lessthan what is required by zoning, while more parkingthan required by zoning is provided. Big box retailparking lots typically have more excess parking thanfor any other land use (Draft Northwest ConnecticutParking Study, Fitzgerald & Halliday, Inc. 2002).

Reducing minimum parking requirements, estab-lishing or enforcing maximum parking lot ratios,reducing parking stall size, and incorporating alternativeinternal geometry or traffic patterns through the use ofone-way aisles and angled parking stalls can reduceparking lot size and impervious cover. Parking demandratios should be based upon site-specific parking gen-eration studies, where feasible (Metropolitan Council,2001). Incorporation of bioretention facilities or otherstormwater treatment devices (i.e., sand filters, vege-tated swales, filter strips) into parking lot design featuressuch as perimeter and median strips can further reducepollutant loads from these areas. Figure 4-4 is aschematic of an alternative parking lot design.

Shared parking is a similar strategy that reduces thenumber of parking spaces needed by allowing adjacentland uses to share parking lots. For shared parking tooperate successfully, the participating facilities shouldbe in close proximity to each other and have peak park-ing demands that occur at different times during the dayor week (Center for Watershed Protection, 1998a).Examples of facilities with different daily peak hoursand potential candidates for shared parking include pro-fessional offices, banks, and retail stores (daytime peakhours) and theaters, restaurants, and bars (evening peakhours). Use of phantom parking is also recommended.Under a phantom parking strategy, sufficient land isreserved for projected parking requirements, but only aportion of the parking area is constructed at the outset.Additional areas are paved on an as-needed basis.

Using Permeable Paving MaterialsPermeable paving materials are alternatives to con-ventional pavement surfaces designed to increaseinfiltration and reduce stormwater runoff and pollu-tant loads. Alternative materials include modularconcrete paving blocks, modular concrete or plasticlattice, cast-in-place concrete grids, and soil enhance-ment technologies. These practices increase a site’sload bearing capacity and allow grass growth andinfiltration (Metropolitan Council, 2001). Stone, gravel,and other low-tech materials can also be used as


FigureFigure 4-3 Alternative Cul-de-sac Design

Path of vehicle overhang

Path of rightfront wheel

Emergencyvehicle

40'

Cul-de-sac withoffset island

A 30' radius willaccomodate mostvehicles and reducepavement

An island can beplaced to allow widerlanes in rear, makingturning easier

Cul-de-sac infiltration island accepts stormwater from surrounding pavement. Note flat curb.

Source: Metropolitan Council, 2001 (adapted from Schueler, 1995 and ASCE, 1990).

30' m

in

20' 20'

24'

40'

20' 20'ISLAND/DRIVING

LANES

20'

8.5'

20'30'


Figure 4-4 Alternative Parking Lot Design Schematic

Transit Stop

Bike Rack

GrassSwale

Crowned withSlope to Swales

TypicalAsphalt

Paving

TurfPavers

OverflowParking

Crowned

Source: Metropolitan Council, 2001 (adapted from Robert W. Droll, ASLA, in Wells 1994).

Curbs withDrain Holes

20'

WideStreet

GroupedPlantings

alternatives for low traffic applications such as drive-ways, haul roads, and access roads.

Porous asphalt or concrete, also known as porouspavement, is similar to conventional asphalt but for-mulated to have more void space for greater waterpassage through the material. Traditionally, porouspavement has had limited application in cold climatessuch as Connecticut due to the potential for cloggingas a result of sand application. Porous pavement hasbeen successfully used for some parking lot applica-tions in New England where the underlying soils aresufficiently permeable. One example is a parkinglot demonstration project at Walden Pond StateReservation in eastern Massachusetts.

While permeable paving materials can makesense in many parking lot designs, site-specific factorssuch as accessibility, soils, maintenance, and long-termperformance must be carefully considered. Permeablepaving materials are most appropriate in areas of lowtraffic volume (e.g., generally less than 500 averagedaily trips or ADT) such as roadside rights-of-way,emergency access lanes, delivery access routes, resi-dential driveways, and overflow parking. ChapterEleven of this Manual contains additional siting anddesign guidance for permeable pavement materials.

4.3.2 Lot DevelopmentThese alternative design practices address thesize, shape, density, and appearance of residen-tial development.

Maintaining Pre-Development VegetationPre-development vegetation should be maintained tothe extent possible. Vegetation intercepts rainfall andpromotes evapotranspiration, thereby reducing thevolume of runoff from a site. Trees and other vegeta-tion can be incorporated into a site by plantingadditional vegetation, clustering tree areas, and con-serving native vegetation. Wherever practical, treesshould be incorporated into community open space,street rights-of-way, parking lot islands, bioretentionareas, and other landscaped areas.

Open Space DevelopmentOpen space development, also known as conserva-tion or cluster development, can reduce the amount ofimpervious area for a given number of lots. Openspace development is a compact form of developmentthat concentrates density in one portion of the site inexchange for reduced density elsewhere (Center forWatershed Protection, 1998a). Planners have advo-cated open space development for many years forcommunity design, preservation of rural character, orcreation of affordable housing. However, it has onlyrecently been identified as a site planning practice forreducing imperviousness and for environmental pro-tection. Open space design is most effective for

reducing impervious cover when used in conjunctionwith narrower streets and other alternative site designpractices. Studies have shown that open space designscan reduce impervious cover from 15 to 50 percentwhen compared to conventional subdivision designs,particularly if narrow streets are utilized (NEMO,1999). Open space designs can generally achieve sig-nificant reductions in impervious cover for mostresidential zones, although only minor reductionsoccur in areas with 1/8-acre lots and smaller (Centerfor Watershed Protection, 1998a).

The benefits of open space development aresummarized in Table 4-4. In particular, this Manualencourages the use of open space development as analternative to conventional subdivision layout to:

❍ Reduce overall site imperviousness and associ-ated stormwater impacts

❍ Avoid development in sensitive areas of a site

❍ Locate stormwater treatment facilities within theopen space

Historically, there have been several barriers tothe widespread use of open space development inConnecticut, primarily due to poorly worded “clusterzoning” adopted by many communities in the 1960sand 1970s. Smaller lot sizes and compact developmentcan be perceived as less marketable, and prospectivehomebuyers may have concerns over management ofcommunity open space. Other common obstacleshave included opposition from adjacent residents dueto concerns about density, traffic congestion, andproperty values. More recent studies have demon-strated that many of these concerns can be addressedthrough thoughtful site design and clear local ordi-nances (Center for Watershed Protection, 1998a).Conservation subdivisions have also been shown tohave marketing and sales advantages, as buyers pre-fer lots close to or facing protected open space.Conservation subdivisions have also been shown toappreciate faster than counterparts in conventionaldevelopments (NEMO, 1999). The Jordan CoveUrban Watershed Monitoring Project in Waterford,Connecticut is expected to provide additional insightinto the benefits of open space development.Recommended sources of additional information onopen space and conservation development are listedat the end of this chapter.

Reducing Building SetbacksReducing building setbacks can reduce imperviouscover. Reducing front yard setbacks results in shorterdriveways. Narrower side yard setbacks may result innarrower lots and shorter road lengths, provided thatnarrower lots do not result in greater overall densityof development. Flexible setbacks and frontage



requirements have been shown to provide attractiveand unique residential subdivisions (Center forWatershed Protection, 1998a). Despite these benefits,the use of flexible setback and frontage distances forreduction in impervious cover has not been wide-spread. Setbacks and frontage requirements aredictated by local ordinances to satisfy various com-munity goals including uniformity of lot size, safety,and traffic congestion. As a result, concerns regardingparking, safety issues, subsurface sewage disposalsystems, livability, and marketability are often imped-iments to relaxed setbacks and frontage widths.Reducing building setbacks is most readily accom-plished along low-traffic streets where trafficcongestion and noise are not a problem (PennsylvaniaAssociation of Conservation Districts et al., 1998).

Limiting Sidewalks to One Side of the StreetSubdivision codes often require sidewalks on bothsides of the street, as well as a minimum sidewalkwidth and distance from the street. Limiting sidewalksto one side of the street can reduce total site impervi-ousness. A sidewalk on one side of the street maysuffice in low traffic areas where safety and pedestrianaccess would not be significantly affected. Sidewalkplans, similar to roadway plans, should be developedby towns to ensure that sidewalks move people effi-ciently from their homes to services and attractions(NEMO, 1999a). Reducing sidewalk widths, separatingthem from the street with a vegetated area, and grad-ing sidewalks away from rather than towards thestreet can reduce impervious area and stormwaterrunoff.

Reducing Hydraulic Connectivity of ImperviousSurfacesImpervious surfaces that are not directly connected tothe drainage collection system contribute less runoffand smaller pollutant loads than hydraulically con-nected impervious surfaces. Isolating impervioussurfaces also promotes infiltration and filtration ofstormwater runoff. Strategies for accomplishing thisinclude:

❍ Disconnecting roof drains and directing flows tovegetated areas or infiltration structures (swales,trenches, or drywells)

❍ Directing flows from paved areas such as drive-ways to stabilized vegetated areas

❍ Breaking up flow directions from large pavedsurfaces

❍ Encouraging sheet flow through vegetated areas

❍ Locating impervious areas so they drain to natural systems, vegetated buffers, naturalresource areas, on-lot bioretention areas, or permeable soils

(Prince George’s County, Maryland, 1999).

Modifying/Increasing Runoff Travel TimeThe peak discharge rate and volume of stormwaterrunoff from a site are influenced by the runoff traveltime and hydrologic conditions of the site. Runofftravel time can be expressed in terms of “time of con-centration” which is the time required for water toflow from the most distant point to the downstream

Table 4-4 Benefits of Open Space Development

Benefit

Reduction of site imperviousness Reduces the cost of future public services needed by the development

Reduction of stormwater runoff and pollutant loads Can increase future residential property values

Reduction of pressure to encroach on resource and buffer areas Reduces the size and cost of stormwater quantity and quality controls

Reduction of soil erosion potential due to reduced site clearing Concentrates runoff where it can be most effectively treated

Reserves large portion of site as green space Provides a wider range of feasible sites to locate stormwater quality controls

Reserves portion of site in open space dedicated to Provides wildlife habitatpassive recreation

Reduces capital cost of development Increases sense of community and pedestrian movement

Provides compensation for lots that may be lost when land is Can support other community planning objectives such as farmlandreserved for resource protection and stream buffers preservation, community preservation, and affordable housing

Source: Adapted from Schueler, 1995.


outlet of a site. Runoff flow paths, ground surfaceslope and roughness, and channel characteristicsaffect the time of concentration. Site design tech-niques that can modify or increase the runoff traveltime and time of concentration include:

❍ Maximizing overland sheet flow

❍ Increasing and lengthening drainage flow paths

❍ Lengthening and flattening site and lot slopes(although may conflict with goal of minimizinggrading and disturbance)

❍ Maximizing use of vegetated swales

(Prince George’s County, Maryland, 1999).

4.4 Low Impact DevelopmentManagement Practices

Low Impact Development (LID), a relatively new con-cept in stormwater management pioneered by PrinceGeorge’s County, Maryland and several other areas ofthe country, is a site design strategy that employsmany of the concepts and practices already describedin this chapter. The goal of LID is to maintain or repli-cate predevelopment hydrology through the use ofsmall-scale controls integrated throughout the site(U.S. EPA, 2000). Site design techniques such as thosedescribed above are one component of the LIDapproach. The other major component of the LIDapproach is the use of micro-scale integrated man-agement practices to manage runoff as close to itssource as possible. This involves strategic placementof lot-level controls to reduce runoff volume and pol-lutant loads through infiltration, evapotranspiration,and reuse of stormwater runoff.

The appropriateness of LID practices is highlydependent on site conditions. Soil permeability, slope,and depth to water table and bedrock are physicalconstraints that may limit the use of LID practices at asite. Community perception and local developmentrules may also present obstacles to the implementa-tion of LID practices, as described previously in thischapter. Although alternative site design and LID prac-tices may not replace the need for conventionalstormwater controls, the economical and environmen-tal benefits of LID practices are well documented (U.S.EPA, 2000). LID practices described in the followingsections include:

❍ Vegetated Swales, Buffers, and Filter Strips

❍ Bioretention/Rain Gardens

❍ Dry Wells/Leaching Trenches

❍ Rainwater Harvesting

❍ Vegetated Roof Covers (Green Roofs)

The main feature that distinguishes these practicesfrom conventional structural stormwater controls isscale. These small systems are typically designed asoff-line systems that accept runoff from a single resi-dential lot or portions of a lot, as opposed to largemultiple-lot or end-of-pipe controls. The followingsections contain summary descriptions of these small-scale LID practices. The design sections of this Manualcontain more detailed guidance for similar,larger-scale stormwater treatment practices such asbioretention, infiltration, and filtration systems.

4.4.1 Vegetated Swales, Buffers, and FilterStrips

Vegetated swales, buffers, and filter strips are vegeta-tive practices that can be incorporated into a site tomaintain predevelopment hydrology. These practicesare adaptable to a variety of site conditions, are flexi-ble in design and layout, and are relativelyinexpensive (U.S. EPA, 2000). Vegetated swales canprovide both water quantity and quality control byfacilitating stormwater infiltration, filtration, andadsorption. Vegetated buffers are strips of vegetation(natural or planted) around sensitive areas such aswetlands, watercourses, or highly erodible soils(Prince George’s County, Maryland, 1999). Similarly,filter strips are typically grass or close-growing vege-tation planted between pollutant source areas anddownstream receiving waters or wetlands. Filter stripsare commonly located downgradient of stormwateroutfalls and level spreaders to reduce flow velocitiesand promote infiltration/filtration. Chapter Eleven pro-vides additional design guidance on these vegetativepractices.

4.4.2 Bioretention/Rain Gardens

Bioretention is a practice to manage and treat stormwa-ter runoff by using a specially designed planting soilbed and planting materials to filter runoff stored in ashallow depression (Prince George’s County, Maryland,1999). Bioretention areas are composed of a mix offunctional elements, each designed to perform differentfunctions in the removal of pollutants and attenuationof stormwater runoff. Bioretention removes stormwa-ter pollutants through physical and biologicalprocesses, including adsorption, filtration, plantuptake, microbial activity, decomposition, sedimenta-tion, and volatilization (U.S. EPA, 2000). The majorcomponents of a bioretention system include:


Figure 4-5 Functional Elements of a Bioretention Facility

Source: Prince George’s County, Maryland, 1999.

Overflowoutlet

Top ofvegetated berm Limit of Disturbance

Sheet flow

Trees

Shrub

Bioretentionarea limit

Grass filter striprecommendedlength 20 feet

Existing edgeof pavement

Grading Limit

A

Ground coveror mulch layer

Plan view (not to scale)

Section A-A (not to scale)

Ground coveror mulch layer

Minimum freeboard0.2 feet from maximumponding depth

Maximum pondedwater depth (specificto plan soil texture)

Grass filterstabilization

Sheet flow

Limit ofpavement

Near verticalsidewalls

Planting soil

Bioretention area

IN-SITU MaterialSaturated PermeabilityGreater than 0.5 inches per hour

2-4' min.

5' min.

3:1 max.slope

A


❍ Pretreatment area (optional)

❍ Ponding area

❍ Ground cover layer

❍ Planting soil

❍ In-situ soil

❍ Plant material

❍ Inlet and outlet controls

Figure 4-5 is a schematic of a typical bioretentionfacility depicting each of these functional elements.Bioretention facilities are most effective if they receiverunoff as close as possible to the source and are incor-porated throughout the site (Pennsylvania Associationof Conservation Districts et al., 1998).

Rain gardens are a small-scale form of bioreten-tion that can be incorporated into a variety of areas innew and existing developments, including:

❍ Residential yards

❍ Street median strips

❍ Road shoulder rights-of-way

❍ Parking lot islands

❍ Under roof downspouts

Rain gardens serve as a functional landscape element,combining shrubs, grasses, and flowering perennialsin depressions that allow water to pool for only a fewdays after a rain (Metropolitan Council, 2001). The soilabsorbs and stores the rainwater and nourishes thegarden vegetation. Rain gardens are an effective, low-cost method for reducing runoff volume, recharginggroundwater, and removing pollutants. Figure 4-6shows examples of several rain garden designs forresidential lots.

4.4.3 Dry Wells/Leaching Trenches

Dry wells are small excavated pits or trenches filledwith aggregate which receive clean stormwater runoffprimarily from building rooftops. Dry wells function asinfiltration systems to reduce the quantity of runofffrom a site. Dry wells treat stormwater runoff throughsoil infiltration, adsorption, trapping, filtering, and bac-terial degradation (Prince George’s County, Maryland,1999). Figure 4-7 shows a schematic of a typical drywell. The use of dry wells is applicable for smalldrainage areas with low sediment or pollutant loadings,and where soils are sufficiently permeable to allow rea-sonable rates of infiltration and the groundwater tableis low enough to allow infiltration. Chapter Eleven con-tains additional design guidance for dry wells.

4.4.4 Rainwater Harvesting

Rain is a renewable resource and is abundant inConnecticut. Rainwater harvesting can be used to sup-ply water for drinking, washing, irrigation, andlandscaping. It generally involves five main compo-nents: catchment, conveyance, purification, storage, anddistribution. Catchment areas are most commonly roofs,while conveyance is via gutters and roof leaders.Rainwater is stored in either rain barrels or cisterns(water tanks). Purification for reuses other than drinkingand washing primarily involves directing the initial flowof runoff, which contains the highest levels of accumu-lated contaminants, away from the storage system.Finally, distribution is through garden hoses or typicalplumbing, depending on the application.

For the purposes of this manual, rainwater harvest-ing can be used to retain a portion of stormwater runoffduring rain events and release it during dry periods suchthat the total volume of runoff is reduced. However,there are additional benefits to harvesting rainwater.Rainwater is generally very soft compared to othersources, as it does not come in contact with soil, andtherefore contains low levels of dissolved salts and min-erals. This makes it preferable for irrigation, gardening,and landscaping. If used for drinking and washing, softwater is less taxing on plumbing and water tanks.

Rain barrels are designed to retain small volumes ofrunoff for reuse for gardening and landscaping. Rainbarrels are applicable to residential, commercial, andindustrial sites and can be incorporated into a site’slandscaping plan. Multiple rain barrels can be used toretain larger volumes of runoff. The size of the rain bar-rel is a function of rooftop surface area and the designstorm to be stored. For example, one 42-gallon rain bar-rel provides 0.5 inch of runoff storage for a rooftop areaof approximately 133 square feet (Prince George’sCounty, Maryland, 1999). Figure 4-8 shows a typicalrain barrel.

Cisterns store larger quantities of rooftop stormwa-ter runoff and may be located above or below ground.Cisterns can also be used on residential, commercial,and industrial sites. Pre-manufactured cisterns come ina variety of sizes from 100 to 10,000 gallons. However,even larger concrete cisterns may be constructed inplace for large industrial, commercial, and public uses.From a stormwater management perspective, the use ofcisterns for commercial development where proposalsinclude high levels of impervious cover, particularly inhighly urbanized areas, should become a more com-monly implemented stormwater management practicein the future.

General design considerations for rain barrels andcisterns include:

❍ Equip rain barrels with a drain spigot with agarden hose threading


Figure 4-6 Residential Rain Gardens

Typical Residential Rain Garden (With and Without Masonry Wall)

Source: Metropolitan Council, 2001 (Adapted from Nassauer et al., 1997) and Low Impact Development Center (www.lowimpactdevelopment.org), 2001.

Front Yard Stone Wall Shrubs Flowers Turf Street

2'-4'

2'-4'

Front Yard Flowers Shrubs in Swale Flowers Turf Street


Figure 4-7 Schematic of Typical Dry Well

Source: Adapted from NYDEC, 2001.

BuildingFoundation

Sump(OPTIONAL)

Mesh Screen

FilterFabric

FootPlate

CleanWashedStone

Observation Well

Cap with Screw Top Lid

12"

Roof Leader

Surcharge Pipe

Splash Block

Access Lid

❍ Use a tight-fitting, light-blocking lid to keep chil-dren and animals out of the water, stop thedevelopment of algae, and limit access to stand-ing water by mosquitoes and other nuisanceinsects. Alternatively, a small mesh screen couldbe used over the hole in the barrel/cistern to limitmosquito-breeding potential

❍ Use a roof washer (collection and disposal of thefirst flush of water from a roof) to catch accu-mulated debris and divert the first flush of runoffaway from rain barrels or cisterns

❍ Use an overflow device to direct excess wateraway from a building’s foundation when thetank is full

❍ Monitor cistern intakes and overflows for blockage

❍ Locate cisterns as close to supply and demand aspossible

❍ Size storage volume based on seasonal rainfalldata and anticipated water requirements

❍ For drinking water supply, purification usingultraviolet light, ozonation, chlorination, reverseosmosis, and carbon filters can be used

4.4.5 Vegetated Roof Covers

Vegetated roof covers, also referred to as “greenroofs”, are layers of vegetation installed on buildingrooftops. Green roofs are an effective means forreducing urban stormwater runoff by replacing imper-meable rooftops with permeable, vegetated surfaces.Rainwater is either intercepted by vegetation andevaporated to the atmosphere or retained in the sub-strate before being returned to the atmospherethrough transpiration and evaporation. Several exam-ples of vegetated roof installations are shown inFigure 4-9.

The green roof is a multilayered, constructed roofsystem consisting of a vegetative layer, media, a geo-textile layer, and a synthetic drain layer. Green roofshave been used extensively in Europe and are becom-ing more common in the United States. A variety ofgreen roof designs exist. The simplest consists of alight system of drainage and filtering components anda thin soil layer, which is installed and planted withdrought-resistant herbaceous vegetation (MetropolitanCouncil, 2001). This type of system is called an exten-sive system. More complex green roof systems such asroof gardens built to accommodate trees, shrubs, andrecreational access are called intensive systems.Figure 4-10 is a schematic of the functional compo-nents of the simpler extensive vegetated roof system.

Recently developed, modular green roof systemsare available for new installations and building retro-fits. These systems consist of interlocking modulescontaining plants that are shipped to the roof site forinstallation. The modules can be removed or replaced,thereby facilitating roof maintenance and repair.

Green roofs are effective in reducing total runoffvolume. For example, simple vegetated roof coverswith approximately 3 inches of substrate can reduceannual runoff by more than 50 percent in temperateclimates (U.S. EPA, 2000). Green roofs not only retainrainwater, but also moderate the temperature of thewater and act as natural filters for any of the water thathappens to runoff (Green Roofs for Healthy CitiesWebsite, 2001). Green roofs in urban areas offer avariety of other benefits such as:

❍ Reduced energy costs by providing building insulation

❍ Conservation of land that would otherwise berequired for stormwater controls

❍ Improvement of air quality by reducing carbondioxide levels and binding airborne particulates

❍ Air temperature regulation and reduction of the“urban heat island” effect

❍ Sound insulation

❍ Improved aesthetics and views from other buildings

❍ Habitat for birds

Design considerations for vegetated roof coversinclude structural and load-bearing capacity, plantselection, waterproofing and drainage, and waterstorage (Metropolitan Council, 2001). Limitations ofgreen roof systems include:

❍ Damage to waterproofing materials may resultin serious roof damage

❍ Can be expensive to design and construct

❍ Sloped-roof applications require additional ero-sion control measures

❍ Higher maintenance than conventional roof

Additional Information Sources

The UConn Cooperative Extension System’s NonpointEducation for Municipal Officials (NEMO) Project. Incollaboration with DEP’s NPS Program, the NEMOProject provides NPS management education andtechnical assistance to Connecticut municipalities freeof charge. NEMO’s goal is to help municipalitiesreduce NPS pollution by understanding naturalresource based planning and how to implement it(http://www.nemo.uconn.edu).

Delaware Department of Natural Resources and theEnvironmental Management Center of the BrandywineConservancy. 1997. Conservation Design forStormwater Management: A Design Approach toReduce Stormwater Impacts from Land Developmentand Achieve Multiple Objectives Related to Land Use.

Connecticut Department of Environmental Protection(DEP). October 2002. Jordan Cove Urban WatershedMonitoring Project. URL:http://www.dep.state.ct.us/wtr/nps/succstor/jordncve.pdf.

Low Impact Development Center. 2002. URL:http://www.lid-stormwater.net/, Revised March 29, 2002.

Natural Resources Defense Council. 1999. StormwaterStrategies: Community Responses to Runoff Pollution.

Puget Sound Action Team. 2003. Natural Approaches toStormwater Management – Low Impact Development in PugetSound. URL: http://www.wa.gov/puget_sound. March 2003.

United States Department of Agriculture (USDA),Natural Resources Conservation Service (NRCS). 2002.Where the Land and Water Meet, A Guide forProtection and Restoration of Riparian Areas. Tolland,CT. March 2002.

United States Department of Agriculture (USDA),Natural Resources Conservation Service (NRCS).Connecticut/Rhode Island Conservation PracticeStandards: #390 Riparian Herbaceous Cover (1998),#391 Riparian Forest Buffer (2001), #570 RunoffManagement System (1997).

Table 4-8 Typical Rain Barrel

Source: Adapted from urbangardencenter.com (D&P Industries,Inc., 2001).

Sealed Lid

Downspout

OverflowOutlet

Garden HoseConnection

4-18


References

Center for Watershed Protection (CWP). 1998a. BetterSite Design: A Handbook for Changing DevelopmentRules in Your Community. Ellicott City, Maryland.

Center for Watershed Protection (CWP). 1998b. RapidWatershed Planning Handbook. Ellicott City, Maryland.

Center for Watershed Protection (CWP). 2000. ThePractice of Watershed Protection. Ellicott City, Maryland.

Connecticut Council on Soil and Water Conservationand the Connecticut Department of EnvironmentalProtection. 2002. 2002 Connecticut Guidelines for SoilErosion and Sediment Control, DEP Bulletin 34.

Fitzgerald & Halliday, Inc. April 2002 (Draft). NorthwestConnecticut Parking Study. Prepared for theNorthwestern Connecticut Council of Governments andLitchfield Hills Council of Elected Officials.

Green Roofs for Healthy Cities Website. 2001.www.peck.ca/grhcc/.

Institute of Transportation Engineers. 1993. Guidelines forResidential Subdivision Street Design, Washington, D.C.

Metropolitan Council. 2001. Minnesota Urban SmallSites BMP Manual: Stormwater Best ManagementPractices for Cold Climates. Prepared by BarrEngineering Company, St. Paul, Minnesota.

New Jersey Department of Environmental Protection(NJDEP). 2000. Revised Manual for New Jersey: BestManagement Practices for Control of Nonpoint SourcePollution from Stormwater, Fifth Draft, May 3, 2000.

Nonpoint Education for Municipal Officials (NEMO).1998a. “Roads”. NEMO Technical Paper #9. Gibbons 1998.

Figure 4-9 Examples of Vegetated Roof Installations

Source: Chicago City Hall (Roofscapes, Inc. 2001) Source: Mashantucket Pequot Museum and ResearchCenter, Mashantucket, Connecticut (Photo courtesyof American Hydrotech, Inc. 1998)

Source: Fencing Academy of Philadelphia(Charlie Miller, Roofscapes, Inc. 1998)

Source: Nonpoint Education for Municipal Officials(NEMO)


Nonpoint Education for Municipal Officials (NEMO).1998. “Addressing Imperviousness in Plans, SiteDesigns and Land Use Regulations”. NEMO TechnicalPaper #1.

Nonpoint Education for Municipal Officials (NEMO).1999. “Conservation Subdivisions: A Better Way toProtect Water Quality, Retain Wildlife, and PreserveRural Character”. NEMO Fact Sheet #9.

Nonpoint Education for Municipal Officials (NEMO).1999a. “Sidewalks”. NEMO Technical Paper #7.

Pennsylvania Association of Conservation Districts,Keystone Chapter Soil and Water Conservation Society,Pennsylvania Department of Environmental Protection,and Natural Resources Conservation Service. 1998.Pennsylvania Handbook of Best Management Practicesfor Developing Areas, prepared by CH2MHILL.

Prince George’s County, Maryland Department ofEnvironmental Resources. 1999. Low-ImpactDevelopment: An Integrated Design Approach.

Schueler, T.R. 1995. Site Planning for Urban StreamProtection. Metropolitan Washington Council ofGovernments, Washington, D.C.

Swift, P., Painter, D., and M. Goldstein. 1998.Residential Street Typology and Injury AccidentFrequency. Swift and Associates. Longmont, Colorado.

Sykes, R.D. 1989. Chapter 31, Site Planning, Universityof Minnesota.

United States Environmental Protection Agency (EPA).2000. Low Impact Development (LID), A Literature Review.EPA-841-B-00-005. Office of Water, Washington, D.C.

Welsh, D. 1991. Riparian Forest Buffers. U.S.Department of Agriculture Forest Service. ForestResources Management. FS Pub. No. NA-PR-07-91,Radnor, Pennsylvania.

Figure 4-10 Schematic of a Typical Vegetated Roof System

Source: Metropolitan Council, 2001 (original source Miller 1998 and American Hydrotech).

Vegetation

Soil medium

Geotextile filter

Synthetic drainage system

Moisture retention & airInsulationRoot BarrierProtective layer

Waterproof membraneRoof surface

Documents

Chapter 4 - portal.ct.gov · Chapter 4 Site Planning and Design 4.1 Introduction ... 4.4.5 Vegetated Roof Covers.....4-17 Volume 1:Background 2004 Connecticut Stormwater Quality Manual