Trees

For Scenic Communities of Mississippi

 

 

 

2005 Urban Forestry Conference

Mississippi Urban Forest Council

164 Trace Cove Drive

Madison, Mississippi

Donna Yowell, Executive Director

 

   

        "Green Laws - Blue Water, And Tree Preservation."

Prof. Buck Abbey, ASLA, CELA

Louisiana State Univeristy, Baton Rouge, Louisiana

        © all rights reserved.

 

"Abstract"            

The urban forestry movement in the past has concentrated on tree biology, tree care, tree rejuvenation and urban forest management matters. Today, and into the future, this movement is expected to take a more holistic view of nature in the city and will see trees as only one element of the fabric of the urban forest.

 

To comprehensively manage the forests of our cities, thinkers and practitioners of urban forestry must deal with a host of urban design and natural resource issues that go beyond tree planting and care that will include a total re-alignment of research that will cover all aspects of nature including, site shading, storm water management, climate modification, urban pest control, storm resistance and urban design problem solving. The scenic values of nature is and obvious aspect of urban design.

 

Among the many issues associated with trees in the city, of is the technology of storm water management. Storm water, soil and trees are naturally compatible so to look at urban trees without paying attention to urban storm water fails to bring a comprehensive view to the urban forest.   Inherent to this broad area of site planning and development are tools, techniques, codes and ordinances that deal with the several aspects of green infrastructure that is important to on site storm water management. Specifically this paper addresses, storm water detentions, retentions, micro-detentions, sand filters, preserved habitats, rain gardens, planted buffers, wetland filters and green parking as measures that should be used by communities wishing to preserve trees to increase scenic values of towns and cities

 

The paper is illustrated with exhibits, appendices, a bibliography and biography of the author.

 

 

 

 

 

                                          

                                             List of Exhibits and Appendices

 

 

Exhibit A-California Model Ordinance Guidelines, Outline

Exhibit B-LSU Tree Ordinance Index

Exhibit C-Chapel Hill, North Carolina, Design Standards Outline

Exhibit D-Collier County, Florida, Sec. 4.06.02.D  Water Management Areas

 

 

Appendix A-LSU Standard Storm Water Management Vocabulary

 

Appendix B-Glossary of Storm Water Best Management Practices

 

Appendix C-Green Laws And Community Design

 

Background Reading On Green Laws

Notes

Biography

 

 

 

 

 

 

 

 

 

 

 

 

 

            “Green Laws and Blue Water”

Nature in the city should be considered as “green infrastructure.”

 

Green infrastructure means that nature’s systems of soils, water, climate, vegetation and wildlife need to be an important aspect of community design and not just something to push out of the way to allow for development. Nature in the city  works for the benefit of society in many ways.  Nature left as an integral part of the urban fabric can clean the air, cool the environment, cleanse the water, stabilize and enrich the soils, reduce damage from storms, provide habitat for urban wildlife, add beauty, tranquility and scenic value and in general raise the biodiversity level and health of inhabitants. 

 

Nature in the city can take many forms.  We find nature in the city as undeveloped land, partially developed land and intensely developed land.

 

In the first instance, nature can take many forms from climax forested land, wetlands, meadows and maturing wood lots. Each of these absorb energy from the sun and can convert it to something useful for society if properly harnessed. Wetlands and maturing wood lots are particularly productive followed closely by meadows and climax forests.  Ecologist’s carefully study this question of productivity and a basic text book such as Odom’s Fundamentals of Ecology^{. 1.} illustrates the importance of nature’s systems in regard to energy conversion, biodiversity and climatic health. This, is the first step in understanding why green infrastructure is important to American cities.  Undeveloped land has mature drainage systems that absorb and infiltrate rain water back into underground aquifers that recharge or potable water supplies.

 

Partially developed land includes agricultural land, park land, forested preserves and low intensity subdivision developments.

 

Within these types of land uses nature is represented by edges, hedge rows, buffers, preserved trees groves, agriculture crops and the home garden. Home gardens in these suburban areas are dominated by the ‘front lawn’ and exotic garden plants are about the least productive natural system within this type of land use.  Lawns do little that is ecologically productive and it can be argued that they subtract from nature’s ability to do work in that mowing, thatching, artificial irrigation, garden chemical and gasoline use is counter productive ecologically. The best that can be said about lawn grass is that it stabilizes soil, can be pretty, and reflects much less solar heat than concrete or other building materials.  

 

But most importantly, these types of developments have an immature drainage system that often excludes natural methods of storm water retention. Many lands within this category rely upon ‘inlet, pipe and headwall drainage systems’ that simply dumps storm water into the closest natural water body available. Where the water goes, the agricultural chemicals, sediments, suburban waste and garden pesticides, insecticides and fertilizers are going to follow. It should be noted however, that it is within this category of land use that ‘low impact development strategies’ and integrated management practices’ are most practical.

 

The third and last category of land use where we find nature in the city are those contrived natural areas found within intensely developed land. These areas are small, disconnected and incomplete natural systems. Only representative of what is truly natural.  In most instances they are designed landscapes and generally consist of such city center amenities as pocket parks, squares, planted bosques, intersection dividers, street tree plantings, building entries, paved and planted terraces, drainage canals, botanic gardens and zoos. Land costs and demand for space within the heavily populated city center generally precludes nature or its natural systems from the scene. If nature is there at all, it has been designed by landscape architects.

 

Drainage systems within intensely developed land uses, such as found within the city center, are always underground inlet, pipe and headwall systems with an occasional river edge, water supply reservoir, lake or retention pond added.  Most storm water is designed to drain off the land, little if any storm water is absorbed where it falls. Parking lots, streets, rooftops and pedestrian walkways will comprise over ninety (90) percent of the area of intensely developed land thereby leaving little space for natural on-site storm water management. ^{. 2.}

 

Nature within the city, whatever form it takes, must do work to make cities, cleaner, healthier and more beautiful. Nature must solve certain problems associated with urban design in order to make community’s ‘smarter,’ scenic and  better places in which to live.

“Landscape Codes”

The way to ensure that nature in the city is cared for is to enact a comprehensive landscape code which specifies minimum standards for caring for nature in the city, that would include design standards site development, land clearing, habitat preservation, tree protection, irrigation, water conservation and on-site storm water management. ^{. 3.}  In recent years, city after city across the nation have turned to this type of ‘green’ legislation as a means of ensuring better site design, acceptable community design, tree preservation and better landscape construction practices within the city. The better codes, are always contained within a community’s zoning ordinance.

 

Landscape codes typically provide for the construction of such site facilities as parking lots, site service area, pavements, urban walls, landscape buffers, irrigation systems, visual screens, compliance with ADA standards and design of yard plantings that serve a variety of uses.  In most communities, the reason for the ordinance is the protection of scenic valures by putting regulation on lot compatibility, damages to natural systems, water usage, and those that provide landscape design, maintenance, arboriculture or landscape construction services.  Communities are also creating standards within ordinance language to protect tree canopy, provide for shade, prevent storm water run off, abate erosion, and cool hot urban environments.

 

Tree ordinances are often stand alone laws that are part of the municipal code but not part of the zoning ordinance. More often than not, they apply only to trees on public land.^.4. Tree management ordinances advocated by such organizations as the International Society of Arboriculture (ISA) set standards for the care of trees in American cities and towns. Many tree laws regulate the practice of arboriculture and set up municipal urban forestry programs, establish ‘tree’ boards and institute licensing for arborist. ^{. 5 .}     

 

From a recent study of fifty community tree ordinances, including those contained within the USDA Forest Service Tree Ordinance Index, it is clear that most contemporary tree ordinances have been written to protect and preserve trees rather than to support the needs of zoning, land use, development and design. ^{. 6 .}   Exhibits A illustrates the most common regulations found in traditional municipal tree ordinances.^{. 7 .}  Some of the more contemporary ordinances found in Exhibit B, the LSU Tree Ordinance Index for instance regulate tree preservation, planting, and habitat preservation.  The older tree ordinances themselves do not affect on site storm water management. It requires more comprehensive codes than laws that onlyi deal with trees. 

 

It is common for tree ordinances to not address zoning, development or design either.  All are measures, strongly related to the development and management of land and tangentially to the urban forest. The better of the contemporary ordinances such as found in Collier County, Florida, Lexington, South Carolina and Fairfax County, Virginia are becoming more integrated with landscape regulations that have become part of municipal zoning regulation since tree ordinances came into popular use in the 1960’s.

 

While many communities enact ordinances merely for beauty or economic development, there are other important reasons why these codes are written.  In recent years, Davis, California enacted a landscape ordinance for solar control, particularly in regards to parking lots.  Near by Irvine, California, enacted an ordinance to promote sustainability which is a form or recycling natural resources and energy. Santa Monica, in Los Angeles country, is known as the ‘sustainable city’ and recovers all rain that falls upon the city in order to recaptures pollutants before they find their way into Santa Monica bay. Trees are an important part of each of these ordinances.

 

Communities in Florida, such as Lake Mary and St. Lucie County, base their ordinances on the need to conserve and reuse irrigation water and to manage storm water on-site. Collier County on the west coast and Volusia County on the east coast both require on-site storm water management and have standards that call for specialized storm water facilities. ( Exhibit D ) Louisiana is exploring on-site storm water management and green parking lot design. Too much water is a problem in Louisiana so the Louisiana Department of Environmental Quality is working on a model landscape code that will help clean the state’s coastal waters. Maryland and Virginia have recognized the same problem for over a decade so many of their local codes call for forest preservation and storm water management. Howard County, Maryland’s code is a good example of how a landscape code can be directed toward forest preservation. 

 

Some of the new Georgia codes are directed toward sustaining tree canopy and preventing soil erosion. These codes call for a certain density of trees on all development sites. Texas codes are being crafted to include more shade within vehicular use areas. Austin recently drafted new language that will make parking lots cooler.  In the Carolinas tree codes are being written to enhance the urban forest canopy by provide for a stated numbers of trees per acre. These codes are concerned with canopy standards, shade requirements and tree preservation. However it is still very common for tree ordinances as we know them to not address storm water.

 

“Storm Water and Integrated Management Practices”

Tree ordinances and landscape codes, both working to preserve, protect and replant nature in the city need to be combined rather than competitive or overlapping. The Chapel Hill Ordinance, ( Exhibit C ) is a good example of how tree ordinances need to be designed to be ‘harmonized’ with landscape codes and storm water management codes.  Chapel Hill, North Carolina’s landscape regulations are based upon “integrated management practices” that combines their tree and landscape requirements into the zoning ordinance in the form of site design standards. These design standards include regulations for critical areas, habitat preservation (especially of ‘significant stands’), tree care, tree protection, landscaping, screening, buffering, parking lot design, open space, integrated management practices, lighting, storm water management and erosion/sedimentation control. They are all integrated into the zoning code where these several green laws work to keep nature in the city.  All tree ordinances need to be contained with zoning laws and must emanate from land use and not be just part of a community’s general body of law that dictates land use from outside the zoning code.  In other words, green laws need to enhance zoning, not just put limits on land development.

 

The first message is that contemporary tree ordinances need to be “harmonized” or woven together to be part of the same body of municipal law. An examination of contemporary vocabulary associated with on-site storm water management gives evidence of the need for integration. ( Appendix A. ) Tree regulations that promote storm water management are essential as a first step in recognizing that green infrastructure is more than just trees. 

 

The second message is tree laws need to be more concerned with root space and storm water infiltration rather than just tree canopy area. When looking at these factors it critical to see how preserved trees fit in with the proposed site plan.  Many newer tree laws focused on tree density are based upon canopy or shadow pattern and not available planting or infiltration area. The Fulton Country, Georgia ordinance is a case in point.^{. 8 .} The purpose of this ordinance is to cultivate and encourage a high level of tree preservation through administrative guidelines rather than implement regulations within the zoning ordinance. The code is designed to provide standards for the preservation of trees as part of the land development, building construction and timber harvest processes. It is not the intent of this ordinance to regulate individual properties that must enhance the rules of zoning. The requirements kick in only when activities require a land disturbance permit, a building permit or timber harvest permit. Storm water management is not part this ordinance. When benefits of the code are cited to the citizens of Fulton County, environmental improvements are mentioned but no design standards are given for control of soil erosion, moderation of storm water runoff, improved water quality, interception of airborne particulate matter and the reduction of air pollutants.  Enhanced wildlife habitat is also mentioned as are the reduction of noise and glare, climate moderation, aesthetics, scenic quality and increased property value. Yet no mention is made of zoning or how the tree preservation ordinance increases the community’s ability to zone effectively for land use, bulk, height, set back, screening, buffering or storm water management. 

 

Finally, even contemporary tree laws and recommendations for their drafting fail to recognize the importance of codes based upon integrated management practices, zoning, site development and design.^.6.  Single issue landscape codes that deal only with trees fail to react to these new trends that are developing in community design. These trends include on-site storm water management, green parking, low impact development, smart growth and new urbanism may completely undo the way we presently think about writing tree ordinances. They offer new possibilities for writing creative harmonized tree ordinances that truly work to protect the many aspects of nature in the city.

 

The best way to insure that trees are seen as green infrastructure is to make sure that tree laws recognize design and are contained within, (harmonized) with landscape codes and landscape regulations both of which are codified within community zoning laws. This will not be an easy task but the trend has started ^{. 9.} Cities such as Mandeville, Louisiana, Collier Country Florida and Southlake Texas are ahead of most communities when it comes to tree preservation. They have good standards and exceptional enforcement.  Other towns and cities such as Baton Rouge, Louisiana;  Columbia, South.Carolina; Fairfax County, Virginiana; Greensboro, North Carolina.; Gwinnett County, Georgia; Howard County, Maryland;  and Marco Island, Florida have enacted  comprehensive green laws that see trees as an important element of zoning that have implications for environment, conservation, storm water management, open space and civic design. This is a positive trend for the future for tree preservation laws.^{. 10 .}

 

Storm Water Management Facilities

On site storm water management language contained with community landscape codes offer additional opportunities to preserve trees and increase scenic values within communities. . Particularly, to storm water management methods inserted with landscape codes preserve native habitat, protect existing groves of trees, allow vegetated filters and provide for the  planting of trees in buffers that also serve as storm water infiltration basins.

 

The fundamental concept behind on-site storm water management is that a certain percentage of all rain fall that drops on any development site must be retained and infiltrated, evaporated, exfiltrated or transpirated on that site utilizing some combination of structural or non-structural storm water management facilities. (Appendix A )  Often called, storm water best management practices, or simply BMP’s, these are methods or constructed site development facilities as seen in Figure no. 1 will often combine all three methods of water transfer to reduce storm water run off and its ability to carry sediments, chemical pollutants and urban waste down stream to fresh water bodies.  In addition to quantity of storm water, the quality of regional water supplies are also greatly effected by urban tree canopy and growing space requirements in regard to nutrient loading, run off and infiltration. ^{. 11.}

_______________ _________________ _________________ ______________

Preserved Wetlands

Constructed Wetlands

Preserved Habitat Preservation Areas, Tree Groves

Micro-detentions

Rain Gardens

Vegetated Filters

Infiltration Trenches, French Drains

Sand Filters

Planted Buffers

Parking Lot Detentions

Stream Side Buffers

Porous Paving and Green Parking

Underground Storm Water Chambers

Disconnected Roof Tops

_________________________________________________________________Figure 1.0.  Landscape Storm Water Management Best Management Practices

These storm water best management practices are best designed for partially developed land found in suburban districts where space is available and development pressures are the greatest.  They are generally not needed in undeveloped land and space limitations restrict their use within intensely developed land of inner cities and central business districts.

 

A brief introduction to each of these is presented below.  Additional details are available in Appendix B which is attached.  It should be noted that Appendix B is a work in progress for the Louisiana Department of Environmental Quality who working on storm water management within the State of Louisiana.  It is very possible to include within a community landscape codes language that will suggest or require the use of the following storm water best management practices. 

 

Preserved Wetlands.  Natural wetlands are nature’s way of handling storm water upon the land.  Wetlands function as collection and filter points for run off that begin at higher elevations on their journey toward  the sea.

 

Wetlands are characterized as vegetated parcels of land that have standing water for part of the year.  If they are wooded they are referred to as a swamp or if they contain no trees they are called a marsh.  Wetlands are also found along gulfs, bays, oceans, streams and on lake edges.  Lakes and open water bodies are not considered wetlands however.

 

The best wetlands for on-site storm water management are those wetlands that can be preserved on existing sites without any alteration or development. Should these wetlands be wooded or covered with a tree canopy, this storm water management area benefits the environment by saving trees at the same time it handles water.

 

Constructed Wetlands.  Natural are created geo-morphologically over time by natural systems evolution while constructed wetlands are designed.  Constructed wetlands are commonly used are large development projects such as golf courses, shopping centers, business parks and industrial sites.  These wetlands may be designed as part of an integrated drainage system built around lakes and ponds that may include detention areas, retention areas or just low soggy depressions that collect and store storm water.

 

As a design water storage and treatment systems constructed wetlands are properly sized, earth graded and planted with native wetland vegetation. Of these three functions, the planting is the most difficult to do under man made conditions.  For wetland vegetation to be successfully designed, it must responds to water depth, salinity and competition from other plants and animals.

 

Preserved Habitat Preservation Areas, Tree Groves. Forest floors are among nature’s most efficient storm water management methods. Rain falling on tree canopy begins to be managed as soon as raindrops fall on leaves. As anyone knows, who has stood under a tree during a light rain storm, very little of the rain actually makes it to the ground. Light rainfall is absorbed, reflected and filtered by the canopy and the massive leaf area of the thousands of leaves that occur on a mature forest tree.

 

Rain that does make it to the ground is immediately absorbed into the forest duff, a thick four (4) to six (6) inch layer of fallen leaves, decaying leaf matter and native soil mulch. Finally, when rain actually gets to the surface soil level it too is quickly absorbed due to the natural porosity of the soil caused by root growth soil insects and ground creatures who mine the soil for food and nutrients.

One of the most effective storm water best management practices that will preserve trees and manage storm water is to preserve natural habitat on development sites. 

 

Micro-detentions. A series of shallow depressions within the graded earthworks of a site that can be designed and constructed to recharge water that falls on developed property directly into the ground rather than letting it flow indirectly into the ditch or a canal along the property. They are commonly located in parking lot islands, adjacent to roadside ditches, within planted buffers or within small pockets of open space within highly congested land uses.  A variant of this, at a much large scale and volume, is the dry detention that is calculated for water volume storage and is used as parking lot detentions as described below.

 

Rain Gardens. These simple site structures or depressions within lawn areas and known as bio-retention traps or rain gardens. They are landscaping features adapted to provide on-site treatment of storm water runoff in highly urbanized areas.. Surface runoff is directed into shallow, landscaped depressions where it may infiltrate, evaporate or be transpired by specially planted wetland plants, which are native to the region.  

 

Vegetated Filters. Common swales carry storm water across a development site to where it is disposed or stored. Vegetated filters are a form of swale that are often called grassed channels or bio-filters because course vegetation is allowed to grow.  Vegetated filters refer to vegetated open channel water management practices designed specifically to treat and attenuate storm water runoff for a specified volume of runoff. Storm water falling on development sites flow through these channels and is treated through vegetation filtering and or filtering through a prepared porous subsoil mix, and/or infiltration into underlying native soils. Vegetated filters, primarily native grasses, forbs, herbs and ground covers lining the channel reduce the flow velocity of concentrated runoff and allow sediments and pollutants to drop out as a result of friction loss.

 

“Louisiana Ditch Gardens” are a variant of this type of best management practice in which swales or roadside ditches are designed to hold shallow amounts of water and are planted with  a variety of showy wetland plants.

 

Infiltration Trenches, French Drains. Infiltration trenches are somewhat a cross between sand filters and vegetative swales.  They are often linear such as swales and they are constructed with the good infiltration capability of sand filters.  Where they differ is in the way they are properly constructed. 

 

Essentially French Drains as they are called in Louisiana, are linear trenches, which are dug to any depth that the amount of storm water flow requires. The concept of sizing is very simple. They are sized large enough and with enough storage capability to store the exact amount of rain expected to fall on the site during any given storm.  They can be sized to pick up WQ (WQ is the first one inch of rainwater, which is typically the most toxic) or even greater storm events.

 

Sand Filters. Sand filters are any number of depressions, trenches, barriers or sand lens constructed of sand that can be used to improve ground water recharge. The primary purpose of this storm water BMP is to improve internal soil drainage in low areas of a park. This is done by taking advantage of the internal flow of capability of sand rather than the native silts and clays which are typical in Louisiana parks. The usual method of construction of this feature is to excavate native soil areas designated in the site plan for this type of drainage feature and backfill with sand over a gravel base. 

 

Planted Buffers. Landscape buffers are areas of development sites often found along property lines that are set aside for planting and screening.  Most landscape buffers, their use, size, extent and character are defined in community zoning regulations. Particularly, in community landscape codes that require buffering and screening between adjacent land uses. However, well-planted buffers may provide other services.  Storm water management zones, sediment traps, wildlife habitat and features of natural beauty are all common functions that can be designed into planted landscape buffers 

 

Planted buffers generally consist of plantings of small trees or large shrubs, be they formal, informal or naturalized and can be designed to soak up rainwater falling on development sites. Planted buffers can have improved internal drainage and can be linked together for maximum storm water collection during WQ rainfall events.   Buffers can be built for storm water management along roadways, at property edges, parallel to walkways and almost any place on a development site in which open space can be found.     

 

Parking Lots Detentions. Perhaps the most important dry detention  areas are set aside to capture run off from large parking lots. These detentions are best used along roadway frontages  where they can add to the open space percentage of development site and store the required volume of water that is generated over the extent of the paved area of the site.  Parking lot detentions may be grassed, may serve as over flow parking or be designed to be contrived plantings that can feature planted buffers, streams or rain gardens.

 

Riparian Buffers. Natural buffers or naturalized plantings along streams, bayous, and lake edges protect water quality by filtering out sediments and pollutants before they can enter a fresh water body. A riparian edge buffer is an administratively protected area along a water body where development is restricted or prohibited. The width of the buffer zone is dependent upon the size of the stream and its drainage load and overflow characteristics.

 

The primary function of buffers is to physically protect and separate a stream, lake, or wetland from development, edge disturbance or encroachment. If properly designed, a buffer can provide storm water management and act as an overflow zone during floods, sustaining the integrity of stream ecosystems and associated riparian habitats.

 

The best riparian buffers are those that are preserved in their natural state.

 

 

Porous Paving and Green Parking. Porous paving that allows the infiltration of storm water is defined by the EPA as green parking. However, this term is very limited in its meaning of green.  A better description of green parking would be one based upon the assumption that a parking lot could provide many beneficial environmental services. In other words, parking lots that do environmental work are green.

 

Green parking design refers to several techniques applied together to reduce the contribution of parking lots to the total impervious cover of a site as well as to provide additional space for planting or preserving existing trees. Green parking is motivated by a storm water management perspective, a planting perspective and an open space design perspective.  And of course earth friendly, low energy impact and sustainable methods and materials should be used in green parking lot design.

 

Green parking lot design carries some of the same connotation as "Green Building Design" which is currently a hot topic with architects, interior designers and eco- builders. Essentially, green buildings are architecture in which materials and systems do not degrade the environment.

 

Green parking lot design contains some of the same ideas. Ideas about on-site storm water management practices, shade generation to, cool hot pavements, vehicle screening as well as ideas about  permeable paving, micro-detention, low impact development, pollution interception, car sorting, pedestrian management, habitat protection, irrigation management and tree preservation within parking areas.

 

Underground Storm Water Chambers . Underground storm water chambers are a structural storm water control method which is manufactured to be effective long-term wastewater management systems. They can easily be adapted for storm water management as well. They are primarily used for underground storage and treatment if necessary. They are viable, low cost, low tech solutions to decentralized storm water drainage capture that has been approved by the EPA since 1997. If they are planned, designed, installed and maintained properly they become a very useful method of storing storm water on-site.

 

In most instances, underground chambers are installed under parking lots to detain, filter and clean sheet flow from concrete, asphalt, rooflines and other impervious surfaces. They can be adapted with special storm water treatment chambers to soak up oils and other human made petrochemical pollutants that are commonly associated with automobile parking areas of horticultural maintained turf grasses.

 

Exfiltration beds of sand and gravel are used to soak up and filter any storm flows not leached back into the ground directly under the chamber line or bed. The filter medium is typically sand, but it can consist of sand, soil, gravel, peat, compost, or a combination of these materials. The purpose of the filter bed is to remove smaller sediments and other pollutants from the storm water as it percolates through the filter medium. Finally, treated flow exits the sediment filter system via an outflow mechanism to return to a storm water conveyance system or a permanent retention pond.

 

Disconnected Roof Tops.

A disconnected roof top is one in which storm water falling on a building roof is captured and prevented from being added to the amount of storm water that potentially could run off the site or be added to an above ground or underground water conveyance system.

 
Disconnecting the rooftop storm water can reduce storm water amounts by a huge percentage, perhaps up to forty percent of the water volume falling on any development site.  At the very least, disconnected rooftops will artificially reduce what storm water engineers call the coefficient of run off. 

 

There are various ways to disconnect the roof top. Perhaps the easiest is to convey the water through an eave and downspout system directly into under storage or filtration trenches where it would be allowed to exfiltrate out or infiltrate into the sub soil. Storm water captured in this way can also be stored in below ground storm water chambers often installed under parking areas. It is even possible to capture the water in an old fashion house side cistern and then use that water to feed and artificial irrigation system.

 

Parking Lot Detentions

Perhaps the most important storm water management feature that can be included within community landscape codes is the parking lot detention.

 

Parking lot detentions are generally dry detention areas that set aside to capture run off from large surface parking lots and roof tops. The detentions are sized to store the required volume of water that is generated over the extent of the impermeable area of the site. A well designed dry detention may be designed to capture as much as ninety (90) percent of all rain that falls on development sites t larger than five (5) acres.  They are also engineered to make sure they do not flood and can trickle out a specified amount of rain water over a proscribed period of time.

 

Parking lot detentions may be grassed, may serve as over flow parking with porous paving or be designed to be of contrived plantings that can feature planted buffers, streams or rain gardens.  Some dry detentions are designed to be patterns of porous stone and gravel

 

These detentions are best used along roadway frontages where they can add to the open space percentage of development site and the visual appearance of the project.  And of course, well designed detentions can add aesthetic value to any development site. They can add beauty and add significant open space to any site if properly sited and designed.  Plantings of trees, shrubs and ground covers upon the lip of the detention, on its side slopes or within its bottom can create color, texture and form that will give striking visual character to what would other wise be an engineered wasted space that is normally seen surrounded by chain link fencing.