CI B K3

Sustainable and Resilient Development Design

protections and practices employed during the site development process that reduce the environmental impact of a project while retaining and enhancing the owner/developer’s purpose and vision for the site

Sustainability

the support of long-term ecological integrity

• Avoiding and minimizing land cover conversion in areas susceptible to erosion

• Preserving areas that provide important water quality benefits + habitat features

• Developing sites in a manner that protects water bodies and natural drainage systems

Sustainable site design practices

mimic predev hydrologic conditions by preserving natural features and reducing impervious cover

• Reduces cost of infrastructure

• maintains/increases value of property

Typical elements of sustainable site design

• Preserving natural areas and native vegetation

• Minimizing disturbance of existing, mature stands of vegetation

• Reducing impact on watershed hydrology

• Incorporating natural drainage pathways as a framework for site design

• Preventing stormwater impacts rather than mitigating for effects

• Managing stormwater quantity and quality as close to source as possible

• Using simple conservation methods rather than structural controls → lower cost/maintenance

• reducing soil compaction during construction

Resiliency

• the ability of a system to respond to, or recover readily from, stresses or disruptive forces

  • New dev should be guided away from known hazards

  • Need to implement practices in new devs that are resilient, strong, flexible

  • Primary goal is to design system that can function in the face of threats/hazards

  • Conserve natural environmental protective systems

Hazard mitigation activities

• Planning to identify hazards + vulnerability

• Implementing smart growth + hazard mitigation plans before disasters occur

• Avoiding known/previously affected vulnerable areas (ex. floodplains)

• Also seeks to address identified hazards w/structural/nonstructural approaches

3 types of recs for more sustainable designs

• Conservation of natural areas

• Appropriate design of streets/parking lots

  • Ex. reducing street lengths/widths

• Appropriate site/lot development plans

• Reduces need for clearing/grading, greeater open space, more canopy, opportunities for conservation initiative

Where do nontidal wetlands occur?

floodplains

• in MS: bogs, swamps, riverbanks, bottomland forests, bayheads, coastal flatwoods, and savannas

tidal wetlands

• found @ edge of coastal waters, provide habitat for birds and a nursery for shrimp + our aquatic life

  • Salt + brackish marshes, freshwater marshes and swamps, mud flats, tidal open water habitats (bayous, rivers, oyster beds, other coastal waters)

  • Common trees: bald-cypress, tupelo gum

MDEQ Erosion and Sediment Control Practice

• emphasizes the importance of protecting intact wetlands and stream channels, provides further information on the regulatory programs in place for their protection

federal CWA Section 404, Rivers and Harbors act of 1899

•  U.S. Army Corps of Engineers (USACE) must issue a federal permit for any actions that impact tidal wetlands, nontidal wetlands, and shallow water habitat. 

• 2 types of permits: general + individual

• Requires developer to take steps to avoid/minimize wetland impacts caused by implementing a project + provide compensatory mitigation for any remaining unavoidable impacts

• Projects requiring Section 404 permit also require section 401 water quality certification from MDEQ

Actions requiring USACE authorization

• Construction of piers, marinas, ramps, cable or pipeline crossings

• Dredging and excavation in or adjacent to waters of the United States

• Fill for residential, commercial, or recreational developments

• Construction of revetments, groins, breakwaters, levees, dams, dikes, and weirs

• Placement of riprap (for channel stabilization) 

National Flood Insurance Program

• for coastal counties — Local govs required to restrict placement of any structure, fill, or obstacle within the floodway of a stream or river 

• Within Mississippi

  • Development in floodplains regulated by county + city floodplain + dev ordinances

Benefits of riparian buffers

• provide filtration for overland flow → retains sediment from up-gradient disturbed areas + after construction

  • flood control

  • Helping protect properties from shifting and widening of stream channels that occur over time

  • Increasing property values

  • Minimizing activities that degrade, destroy, or reduce the value and function of coastal marshlands 

  • Enhancing scenic value and recreational opportunities of wetlands

  • Protecting coastal habitat for nesting and feeding wildlife

  • Protecting important nursery areas for fisheries, which provide food and habitat to numerous species of fish and shellfish, including commercially important species 

  • protect waterways + aquatic resources from short + long term impacts of dev

  • extend important protection to narrow corridors

  • provides greater habitat connectivity w/nearby tidal marshes + open waters

Site Assessment

an in-depth evaluation of the eco conditions + natural features present @ the proposed dev/redev site + is conducted prior to developing a detailed site design

• Conditions/features to investigate:

  • Wetlands

  • Floodplains

  • Riparian areas, streams, and other waterways

  • Soil types, infiltration capability, and soil erodibility

  • Mature forests and other woodlands

  • Types and health of other existing vegetation (trees, shrubs, grasses, and forbs)

  • Prominent landforms

  • Steep slopes

  • Depression storage

  • Aquifer recharge areas

Green infrastructure

• managing stormwater close to its source and using nonstructural methods for stormwater management

  • uses vegetation + soils to manage stormwater via infiltration, evaporation/transpiration , and rainwater capture and reuse

Gray infrastructure

uses built structures such as concrete curb + gutter systems, pipes, and retention basins

Low-impact Development (LID)

focuses on managing rainfall @ source, using distributed, decentralized small-scale controls on the lot level that mimic natural hydrology

• Key elements:

  • Conservation

  • Small-scale control

  • Customized site design

  • Pollution prevention and education

  • Directing runoff to natural areas

• Result in ~25-30% reduction in costs associated w/site development, stormwater fees, and maintenance for residential developments 

EPA Water Quality Scorecard

• Help local govs id opportunities to protect water quality by removing barriers + revising/adopting pertinent codes, ordinances, incentives

• Offers resources for: 

  • Protecting natural resources + open space

  • Promoting efficient, compact dev patterns + infill

  • Designing complete, smart streets that reduce overall imperviousness

  • Encouraging efficient parking areas

  • Adopting green infrastructure stormwater management provisions

Conservation design

laying out elements of a dev project to take advantage of a site’s natural features + preserve sensitive areas, while also considering site constraints + opportunities to prevent/reduce enviro impacts

• Techniques:

  • Preserving undisturbed areas

  • Preserving stream buffers

  • Reducing clearing and grading

  • Locating projects in less sensitive areas

  • Reducing front and side yard setbacks

  • Aggregating shared open space rather than focusing on individual yards

  • Clustering built features to minimize the amount of disturbed area

Infiltration Practices

• Infiltration basins, trenches, or dry wells

• Highly applicable for roadway projects

• Design Criteria

  • Pretreatment upstream (filter strips, grassed swales, concrete sumps, forebays)

  • Should be designed to completely drain within 72 hrs of the end of a rainfall event

  • Underlying native soils must have infiltration rate of 0.52 in+

  • Distance from bottom of infiltration practice to top of water table should be 2 ft+

  • Observation wells used to monitor percolation + performance of practice

  • Do not place under pavement/concrete

infiltration practices advantages

• Helps restore pre-dev hydrology on dev sites, reduces post-construction stormwater runoff rates + volumes

• Provides v high level of removal for all pollutants

• Provides for groundwater recharge

• Good for small sites w/well-draining soils

• Can be integrated into dev plans as landscaping features

infiltration practices disadvantages

• Can only be used to manage runoff from relatively small drainage areas of 5 acres or less

• Potential for groundwater contamination

• High clogging potential, shouldn’t be used on sites w/fine-particle soils in drainage areas

• Should not be located where they undermine foundations or negatively affect underground utilities/other infrastructure

• Geotechnical testing required, 2 borings per practice

Permeable Pavements

• Water infiltrates into crushed stone bed + infiltrates into soil below

• If native soils have low permeability, perforated underdrain can be provided to collect water + convey it to downstream conveyance system

• 3 primary types: permeable pavers, pervious asphalt pavement, pervious concrete pavement

• Design Criteria

  • Subsurface reservoirs to hold runoff volume from 1-inch storm event

  • Use of underdrain in low permeable soils

  • Underdrain + liner if infiltration not desired

  • Terrace subgrade base/use underdrains for slopes >2%

permeable pavements pros/cons

• Advantages

  • Reduced runoff

  • Improved water + air quality

  • Reduce heat island effect

• Disadvantages

  • Should not be used in hot spots

  • Should not be used on high-volume or high-speed roadways

  • Do not use in areas that may receive high sediment loads

  • Should not be used where hazardous materials may be loaded, unloaded, or stored

Bioretention Cell

• a depression in the ground filled with soil media mixture and planted with vegetation that can tolerate inundation and dry periods

  • Contain underdrain system allowing filtered stormwater to exit the system

  • Design Criteria

    • Drainage area 5 acres or less

    • Media depth 2-4 ft

    • The permeability of the filter media should be between 1 and 6 inches per hour, and 1-2 in/hour is preferred

    • Ponding depth should be 12 inches or less (9 inches is preferred)

    • Provide an overflow or diversion structure to bypass larger flows around the bioretention cell

    • Design with an upturned underdrain to provide internal water storage volume and enhanced water quality and infiltration

  • Advantages/benefits

    • Removes many diff types of pollutants

    • Good for small areas w/high impervious cover

    • Good retrofit capability

    • Aesthetic feature

  • Disadvantages

    • Areas w/steep slopes

    • Soils may clog over time 

    • Landscaping plan required

Stormwater Planters

• container or enclosed feature located above ground or below ground, planted w/vegetation that collects + treats stormwater through layers of mulch, soil, and plant root systems where pollutants such as bacteria, nitrogen, phosphorus, heavy metals, oil, and grease are retained degraded, and absorbed. 

  • Design criteria

    • Plant w/native vegetation

    • Captured runoff should drain out in 24 hours

    • Structural elements of planters should be stone, concrete, or brick

    • Requires use of underdrain

    • A maximum ponding depth of 6 in is recommended 

stormwater cell pros/cons

Advantages/Benefits

• Reduced stormwater runoff volumes, flow rate, and temperature

• Treats runoff

• Wildlife habitat + aesthetic benefits

• Requires limited space

• Flexible for use in areas of various shapes + sizes

• disadvantages/limitations

  • Small size limits stormwater quantity/quality benefits 

  • High installation cost

  • Can only receive runoff from small drainage areas

Grassed Swales

• vegetated, open-channel management practices designed specifically to treat + attenuate stormwater runoff for a specified water quality volume

  • Designed w/filter bed that may overlay underdrain system

  • Design Criteria

    • Treats runoff for small drainage areas of <5 acres

    • Should be used on slopes <4% (1-2% recommended)

    • Provide storage volume equal to runoff volume from 1st 1-in rainfall

    • Small forebay/pea gravel diaphragm needed for pretreatment wheere water enters swale

    • Min 2 ft clearance between swale bottom + groundwater

  • Advantages/benefits

    • Good for linear eenvironments

    • Lower cost

    • Aesthetic benefits

  • Disadvantages

    • Design depended on site conditions + topography

    • Potential for bottom erosion + sediment resuspension

Rain Gardens

• shallow depressions planted w/native veg to capture + treat runoff

  • Can be planted w/groundcover, grass, shrubs, or trees

  • Design Criteria

    • Sizing based on drainage area

    • Infiltration testing required, avoid compacted soils

    • Plant w/native veg

    • No underdrain required

  • Advantages

    • Reduced runoff

    • Requires limited space

    • Aesthetic

  • Disadvantages

    • Small

Vegetated filter strips

• grassed surfaces designed to treat sheet flow from adjacent surfaces

  • Often used for pretreatment

  • Design Criteria

    • At least 25 ft long

    • Pea gravel diagram @ top of slope

    • Slope btwn 2-6%

    • Groundwater >2ft deep

    • Grass should withstand high-velocity flows + both wet + dry periods

  • Advantages

    • Good pretreatment for other stormwater practices

    • Best for treating runoff from roadways, roof downspouts, v small parking lots if sheet flow can be maintained

    • Low cost alternative

    • Groundwater recharge

  • Disadvantages

    • Concentrated flow within filter strip receivee little to no pollutant removal → must maintain sheet flow

    • Poor retrofit options b/c of space requirements

    • Requies periodic maintenance to prevent channelization

Constructed stormwater wetland

• Temporarily store stormwater runoff in shallow pools that support emergent + riparian vegetation

• Design Criteria

  • Sufficiently large drainage area/adequate groundwater/surface water supplies to provide year-round hydration (~25 acres)

  • Upstream slope <15%, local slopes relatively shallow

  • Elevation drop from inlet to outlet should be at least 3-5 ft

  • 6 components: inlet, deep pool, shallow water, shallow land, upland, outlet

• Advantages/benefits

  • High removal rate for pollutants

  • Wildlife habitat, aesthetic benefits

  • Good for areas w/flat terrain + high groundwater

• Disadvantages

  • Requires large land area

  • Requires continuous baseflow for viable wetland

  • Difficulties in establishing veg + maintaining permanent pool

  • Potential escalated mosquito pop

Stormwater Ponds

• Constructed basins that have permanent pool of water throughout the year

• Water mixes with + dilutes initial runoff from storm events

• 2 primary configurations of stormwater ponds that achieve 80% TSS removal:

  • Wet pond: permanent pool volume equal to runoff from 1st in of rain

  • Wet extended detention pond: smaller permanent pool, temporary storage volume above permanent pool to hold + release runoff over 2 days

• Design criteria

  • Sufficient inflow to maintain permanent pool

  • Upstream slope should not exceed ~15%, local slopes should be relatively shallow

  • 4 design features: pretreatment, permanent pool, outlet structure, safety features

  • Depth of permanent pool should not exceed 8 ft

  • Side slopes to pond should not exceed 3:1 w/o safety precautions

• Advantages

  • Moderate to high removal rate for urban pollutants

  • High community acceptance

  • Opportunities for wildlife habitat and aesthetic benefits

• Disadvantages

  • Requires large land area

  • May pose safety hazards

  • Potential for thermal impacts/downstream warming

  •  Potential for increased mosquito population

Potential Erosion + Sediment Problems Associated with Land Development

• Dev activities expose disturbed soils to raindrops + storm runoff

  • Negative effects on physical properties of soil, onsite drainage + storm runoff patterns, off-site stream/stream-flow characteristics

• Hazards associated w/development:

  • Increase in developed areas exposed to storm runoff/soil erosion

  • Increased runoff, accelerated soil erosion + sediment yield + higher peak flows caused by:

    • Removed veg cover

    • Exposure of more erodible underlying soil/geo formations

    • Reduced cap of exposd soil to absorb rainfall b/c of compaction

    • Enlarged drainage areas b/c of grading oprations, diversions, street construction

    • Prolonged exposure of unprotected disturbed areas b/c of scheduling problems/delayed construction

    • Shortened times of concentration of surface runoff from altering slope steepness, length, surface roughness + installation of “improved” storm-drainage facilities

    • Increased impervious surfaces

  • Creation of exposures facing south + west that may hinder plant growth b/c of adverse temp + moisture conditions

  • Exposure of subsurface materials that are rocky, acidic, droughty, or unfavorable to vegetation

Erosion + Sediment Control

• Leave existing vegetation that doesn’t need to be disturbed → minimize disturbance

• Minimize period of bare ground by shortening construction periods + staging project when possible

• Sequence installation for shortened construction periods + permits the use of temporary/permanent seeding when most effective

• Use sediment control + turbidity measures that minimize sediment/turbid water from leaving disturbed site

• Plan appropriate erosion ctrl for all kinds of erosion that may occur

• Install erosion-control plantings

• Prevent sediment from leaving construction site during muddy periods

• Maintain practices, regular + timely practices

Stormwater Problems Associated w/Land Dev

• First flush”: washing action that stormwater has on accumulated pollutants in the watershed

• In early stages of a runoff rain-event, land surfaces are flushed clean by stormwater

  • Creates shock loading of pollutants

  • Amt of runoff that creates “first flush” depends on activity, site conditions + pollutants

  • Treatment of first flush → minimized WQ impacts of stormwater

• Value of hydrologic environment as an amenity affected by 3 factors:

  • Stability of stream channel

  • Accumulation of trash

  • Disruption of stream community

• Channel that is gradually enlarged from increased floods due to urbanization → decreased visual atractivenss, addition of nutrients/organics/sediment, etc

Historic vs current stormwater management

• Historically, stormwater management was only designed for safety + convenience

  • Goal was to remove runoff as quickly as possible

• Now, management is much more comprehensive

  • Objectives: flood ctrl, nonpoint source pollution ctrl, off-site erosion ctrl

  • Need to ensure volume, rate, timing, and pollutant load of runoff after dev are similar to those that occurred before dev

    • Use coordinated system of source controls: emphasize prevention/reduction of NPS + excess stormwater flow before it ever reaches a collection system/receiving waters

Flood Control

• Historically most common goal of stormwater management

  • b/c increased stream flooding → prop damage, safety hazards, etc

  • 2 levels of drainage systems must be considered: primary + major

  • Primary drainage system

    • Consists of street gutters + ditches, storm sewers, culverts, and open channels that are designed to prevent inconvenience and minor property damages from relatively frequent storm events

    • Should be planned + designed in advance

      • But most are implemented on “as needed” basis → capacity becomes inadequate w/upstream dev

      • Can replace/modify elements of primary drainage system but expensive, doesn’t address problem

      • Can have new dev required to ctrl runoff from their sites in  way that won’t affect downstream drainage system w/stormwater detention criteria

    • Typical detention criteria

      • Specify stormwater runoff from new dev must be controlled so that post-dev peak runoff rate doesn’t exceed pre-dev peak rate for some specific frequency design-storm/range of design-storm events (usu 10 yr)

        • Requiring slower release rates will also req larger storage volumes in detention systems

Major drainage system

• Comes into play when cap of primary drainage system is exceded

• Consists of floodplains + surface-flow routes that water will follow during major storms

• Most effective strategy = ensure stormwater has a route to follow that won’t cause major prop damage/loss of life

  • Use floodplain ordinances, zoning regulations, or other land-use controls to restrict floodplain dev

NPS control

• Goal of controlling NPS is relatively new

• Likely highest priority in watersheds that feed public water supplies or recreation reservoirs

• In urban areas, mos stormwater detention practices used to ctrl runoff quantity may also be adapted for use as BMPs for NPS

  • Slightly diff design criteria - goal tto maximize detention time of captured runoff

    • Basin-drawdown times btwn 30-40 hrs → significant pollutant removal

Off-site Erosion Control

• Similar strats to flood control, differs in frequency of storm that must be controlled

• Most natural stream channels formed w/bank-full cap to pass runoff from storm within 1.5-2 yr recurrence interval

  • w/upstream dev, volume + velocity of flow from relatively frequent storms increase → increased flooding

  • Stream channels often subject to 3-5x increase in frequency of bank-full flows in typical urbanizing watershed

    • Places stress on channel to adjust shape + alignment to accomodate increased flow

    • Adjustment usu happens in short tim

    • vegetated meandering streams become straight, wide, + barren → prop damage, channel degradation

    • Historically used channel mods to increase carry cap/stabiity of streams

      • But controversal, requires special permits

    • Recent innovations based on natual stream-hydrology concepts are becoming more popular

    • On-site stormwater detention criteria for new dev projects can also be used for more frequent storm events

• Multiple-Purpose Criteria

• Stormwater can be managed to accomplish all 3 goals simultaneously

  • Ex. stormwater-detention basin can be designed as multipurpose structure by incorporating diff release rates @ diff stages

Principles of Stormwater Management

• First step should be basing land-use planning decisions based on site planning principles

• Stormwater-management system for each dev project should be based on/support a plan for entire watershed

  • Should mimic/use features + functions of natural drainage system

  • Need to map + id existing natural systems

  • Use “natural” engineering techniques to maximize enviro/econ benefits

• To approximate pre-dev conditions:

  • Maintain perviousness to greatest extent possible

  • Rate of runoff shoulld be slowed

• Maximize on-site stormwater storage

  • Runoff should be routed over longer distance for increased infitration/evaporation, allow suspended solids to settle, + remove pollutants before entering water bodies

• Stormwater management systeems should be planned in advance of the facilities that will discharge into them

  • Design beginning w/outlet for the project

  • Downstream conveyance system should be evaluated to ensure it has sufficient cap for design discharge

  • Restricted outlet = common problem, causes stormwater to back up → use more than one outlet or increase on-site storage volume

• Stormwater should be considered an asset – has potential for irrigation, recreational lakes, groundwater recharge, industrial cooling, etc

• Use multiple-use, temporary storage basins when practical

• Shorelines should be sinuous → increased space for growth of shoreline veg, providing for greater pollutant filtering + increaseed/diversified aquatic habitat

benefits of vegetative cover

• protects soil surface from raindrop impact, scouring overland flow, decreases erosive cap of flowing water by reducing its velocity

  • Reduced moisture content of soil via transpiration → increased cap to absorb water

  • Reduced heat reflectance + dust, increase prop value

• Need to consider effectiveness for soil stabilization + aesthetics when selecting plants (prioritize natives)

• Need grasses/legumes that grow close together to stabilize disturbed sites

• Trees for long-term soil + water protection, not for concentrated flow areas

Site Planning for Tree Protection

• Tree protection measures should be extended from trunk to edge of dripline to protect roots from compaction

  • Can also use tree wells?

• Construct sediment basins in natural depressions

• an imaginary circle on the ground directly beneath the tips of the outermost branches. This perimeter is where the majority of natural rainwater drips off the canopy, and it marks the critical root zone where fine feeder roots absorb most of a tree's water and nutrients

The Stormwater Chain

path of rainwater from highest (rooftops) to lowest point (water body)

Cisterns

• large containers that store water (ex. Rain barrels)

• Rainwater has less salts (chlorine, fluorides) than tap water → using rainwater prevents salt buildup + burning on salt-sensitive plants

• Any material that holds liquids can be used

• Avoid transparent containers to prevent algae buildup

• Can install first-flush diverter if catching water from downspout or roof – prevents contaminants from first flush from going into tank

• Can also bury cisterns in ground + get water via pump

Detention ponds

• temp water storage

  • Protect against flooding + erosion, help settle sediments

  • Ex. rain gardens, biofilters

  • Not created to hold large amts of water for extended periods of time

Retention pond

• landscape feature that holds water for extended period of time

  • Ex. ponds, water gardens

Rain Gardens

• Should have surface water for only a few days (not long enough for mosquitoes to mature)

• Best located in main drainageways on property or in lower depressions

• Considerations:

  • Contact utility company to avoid buried lines/pipes before excavating for garden

  • Do not place near septic drainage fields

  • Place downslope from any structure, avoid building foundations

  • Select areas open/away from large trees

  • Avoid steep slopes (>12%)

  • Sandy soils usu best for allowing water to drain into surrounding soil (need to drain at least 1 in/hr)

Biofilters

• Similar to rain gardens but linear, constructed deeply to handle more water volume

• Good for storing + cleansing water in parking lots or other impermeable paving areas

• Microbes break down organic components + release nutrients when water filters through soil

• Cleans silt + pollutants from first flush

Dry Swales, Dry Creeks, and Drainageways

• Drainage swales designed to be more attractive + carry water safely (compared to roadside ditches)

• Dry Swales

  • Dry for much of the year, only tmep contain water after rain

  • Shallow drainge areas sized to accomodate max water lvls

  • Can use turfgrass in sunny areas to stabilize soils

  • For shady, dry swales:

    • Swamp red maple

    • Bald cypress

    • Green ash

    • Dwarf palmetto

    • Chokeberry

    • Buttonbush 

    • Etc

Green Roofs

• Live plants + growing media installed on roof along w/impermeable membranes + drainage

• Benefits: 

  • Reduces summer temps by up to 20 degrees

  • Absorbs rainwater + reduces runoff

  • Reduces traffic + other urban noises

  • Additional habitat for birds/animals

  • Protects roof from sun exposures + temp fluctuations

  • Additional insulation for building interiors

  • Usually separation layer directly on rooftop, then layers of insulation, moisture barrier, waterproofing, drainage protection, drainage, filter fabric, growing media, plants

  • Slope of roof should be 5-20 degrees

  • Avg nat cost is $8/sq ft

Intensive green roofs

• Growing media 8-24 in, allows for inclusion of larger shrubs/trees

• Need more regular maintenance, for structuress that can support heavier loads

Extensive green roofs

• Shallower (2-7 in)

• Herbaceous pants, ground covers

• Better for existing roof types b/c lighter

• Less maintenance