Low Impact Development


22 févr. 2014 (il y a 3 années et 1 mois)

47 vue(s)

Low Impact Development
& Nonpoint Source

Define Low Impact Development

LID is an approach to land development (or re
development) that works with
nature to manage storm water as close to its source as possible.

LID employs principles such as
preserving and recreating

natural landscape
features, minimizing effective imperviousness to create functional and
appealing site drainage that treat storm water as a resource rather than a waste

There are many practices that have been used to adhere to these principles
such as
bioretention facilities, rain gardens, vegetated rooftops, rain
, and
permeable pavements

By implementing LID principles and practices, water can be managed in a way
that reduces the impact of built areas and promotes the natural movement of
water within an ecosystem or watershed.

Applied on a broad scale, LID can maintain or restore a watershed's hydrologic
and ecological functions.

Nonpoint Source Pollution

Excess fertilizers, herbicides, and insecticides from agricultural lands
and residential areas

Oil, grease, and toxic chemicals from urban runoff and energy

Sediment from improperly managed construction sites, crop and forest
lands, and eroding stream banks

Salt from irrigation practices and acid drainage from abandoned mines

Bacteria and nutrients from livestock, pet waste, and faulty septic

Atmospheric deposition and hydromodification

Nonpoint Source Pollution cont.

Comes from many diffuse sources such as rainfall or
snowmelt moving over and through the ground

Results from land runoff, precipitation, atmospheric
deposition, drainage, seepage, or hydrologic

Impacts of land use on watersheds

Land uses from any part of the watershed

such as
polluted runoff from farms, forests and homes

affect the health of the whole watershed.

Land use practices such as
clearing land for timber or
agriculture, developing and maintaining roads,
housing developments, and water diversions

may have
environmental consequences that greatly affect stream
even when the activity is not directly
associated with or near a stream

Proper planning and adequate care in implementing
projects can help ensure that one activity within a
watershed does not detrimentally impact the downstream

In a healthy watershed, after a rain event, vegetation and
wetlands intercept and slow the flow of water as it travels
through the watershed, removing sediment and allowing large
quantities of water to enter the soil and percolate into the

This groundwater is then available to contribute to late season
stream flow, to the benefit of fisheries and water quality.

In comparison, a watershed with more impervious surfaces and
the loss of vegetation and wetlands, responds differently after a
rain event.

More water runs over the land instead of replenishing

This larger volume of water quickly reaches water bodies
reducing the time available for the water to be cleansed and
filtered and also causing erosion of stream banks.

Most human activities and development have the potential to
adversely affect the overall health and quality of a watershed.

Timber harvest

on unstable slopes can cause erosion.

Agricultural activities

can increase levels of harmful bacteria
and overload runoff with nutrients.

Also, poorly planned
urban and industrial growth

can cause
many of the same problems as farming and timber harvest in
addition to contamination from toxic chemicals.

Even seemingly harmless activities such as
rural development
and recreational activities

along rivers and creeks can be
harmful, impacting the watershed's sensitive riparian vegetation
which is important for water quality protection and wildlife

When viewed individually, most human activities have
little effect on the general health of the watershed.

However, the effects of numerous activities within a
watershed are cumulative and when combined can greatly
diminish the watershed's overall health.

Every activity has the potential to impact the area of the
watershed downstream.

As people place more demands on a watershed,
greater efforts must be made to reduce these
cumulative effects.

Having clean water will require communities to work
together to ensure that activities do not negatively impact
those downstream.

In the 2000 National Water Quality Inventory, states reported that
agricultural nonpoint source (NPS) pollution

is the leading source
of water quality impacts on surveyed rivers and lakes, the second
largest source of impairments to wetlands, and a major contributor to
contamination of surveyed estuaries and ground water.

Agricultural activities that cause NPS pollution include poorly located
or managed animal feeding operations;
overgrazing; plowing too
often or at the wrong time; and improper, excessive, or poorly
timed application of pesticides, irrigation water, and fertilizer.

Pollutants that result from farming and ranching include
nutrients, pathogens, pesticides, metals, and salts

Impacts from agricultural activities on surface water and ground water
can be minimized by using management practices that are adapted to
local conditions.

Many practices designed to reduce pollution also increase productivity
and save farmers and ranchers money in the long run.

Did you know that runoff from farms is the leading
source of impairments to surveyed rivers and lakes?

There are many government programs available to help farmers and
ranchers design and pay for management approaches to prevent and
control NPS pollution.

For example, over 40 percent of section 319 Clean Water Act grants
have been used to control NPS pollution from working farms and

Also, many programs funded by the U.S. Department of Agriculture
and by states provide cost
share, technical assistance, and economic
incentives to implement NPS pollution management practices.

Many local organizations and individuals have come together to help
create regional support networks to adopt technologies and practices to
eliminate or reduce water quality impacts caused by agricultural

Conventional Development vs.

Conventional development techniques often clear all
trees and valuable topsoil from a site and re
grade it so
that all water ends up in one large detention basin.

Resulting problems include
loss of recharge,
increased water temperature, decreased water
quality and higher runoff volumes

The LID approach protects the natural ability of the
site to capture precipitation, keep it clean and allow it
to recharge the local water table.

LID Best Management Practices and
selection criteria

The use of best management practices to reduce the
amount of impervious surfaces, disconnect flow paths
(i.e., downspouts connected to storm sewers), and
treat storm water at its source all help
minimize the
impacts to water quality and local hydrology

Pro’s of applying LID

Provides energy at an affordable cost

Minimizes land clearing and grading costs

Reduces infrastructure costs (streets, curbs, gutters,

Reduces storm water management costs (reduces or
eliminates storm sewers and ponds)

Increases lot and community marketability

Increases lot sale yields and reduces permit fees

Pro’s cont.

Protects site and regional water quality by reducing sediment,
nutrient, and toxic loads to water bodies

Balances growth needs with natural resource protection

Reduces municipal infrastructure and utility maintenance costs
(streets, curbs, gutters, sidewalks, storm sewers and ponds)

Fosters public/private partnerships

Provides local accessibility to open spaces, recreation and
wildlife areas

Preserves and protects amenities that can translate into more
saleable homes and communities

Provides shading for homes and properly orients homes to help
decrease monthly utility bills

Pro’s cont.

Preserves integrity of ecological and biological systems

Protects site and regional water quality by reducing
sediment, nutrient, and toxic loads to water bodies

Reduces impacts to local terrestrial and aquatic plants and

Preserves trees and natural vegetation

Creates connected corridors of wildlife habitat


Supplies have to be specially ordered

Not significantly different compared to what we
already have

Not well known

People refuse to use it.

Hydrologic Controls

Clustering buildings

Building set backs

Naturally vegetated buffers

Natural vegetation should be preserved

Steep slopes should not be disturbed

Rain gardens

Bio retention areas

Grassed swales

Native plant landscaping

Hydrologic Controls

Permeable or porous pavement

Reduced in impervious surfaces

Disconnected down spouts

(Rain barrels)

Green roofs

Rain Garden

Green roof system

What can communities do?

Start using LID for community building/municipal

Make laws to enforce LID

Promote LID

Encourage others to use LID

Reach out to developers

Get projects on the ground

Make sure ordinances are LID friendly

Use less pavement

Soils, wildlife, forestry, and aquatics affect and
are affected by nonpoint source pollution and its
reduction and LID

Polluted storm water runoff can have many adverse effects on plants,
fish, animals, and people.

Sediment can cloud the water and make it difficult or impossible for
aquatic plants to grow.

Sediment also can destroy aquatic habitats

Excess nutrients can cause algae blooms. When algae die, they sink to
the bottom and decompose in a process that removes oxygen from the

Fish and other aquatic organisms can’t exist in water with low dissolved
oxygen levels.

Bacteria and other pathogens can wash into swimming areas and create
health hazards, often making beach closures necessary.


plastic bags, six
pack rings, bottles, and cigarette

washed into water bodies can choke, suffocate, or disable
aquatic life like ducks, fish, turtles, and birds.

Household hazardous wastes like insecticides, pesticides, paint,
solvents, used motor oil, and other auto fluids can poison
aquatic life.

Land animals and people can become sick or die from eating
diseased fish and shellfish or ingesting polluted water.

Polluted storm water often affects drinking water sources. This,
in turn, can affect human health and increase drinking water
treatment costs.

Auto care

Washing your car and degreasing auto parts at home
can send detergents and other contaminants through
the storm sewer system.

Dumping automotive fluids into storm drains has the
same result as dumping the materials directly into a
water body.

Lawn care

Excess fertilizers and pesticides applied to lawns and
gardens wash off and pollute streams.

In addition, yard clippings and leaves can wash into
storm drains and contribute nutrients and organic
matter to streams.

Septic Systems

Leaking and poorly maintained septic systems release
nutrients and pathogens (bacteria and viruses) that
can be picked up by storm water and discharged into
nearby water bodies.

Pathogens can cause public health problems and
environmental concerns.

Pet waste

Pet waste can be a major source of bacteria and excess
nutrients in local waters.

Dirt, oil, and debris that collect in parking lots and
paved areas can be washed into the storm sewer
system and eventually enter local water bodies.

Erosion controls that aren’t maintained can cause
excessive amounts of sediment and debris to be carried
into the storm water system.

Construction vehicles can leak fuel, oil, and other
harmful fluids that can be picked up by storm water
and deposited into local water bodies.

Improperly managed logging operations can result in
erosion and sedimentation.

Uncovered fueling stations allow spills to be washed
into storm drains.

Cars waiting to be repaired can leak fuel, oil, and other
harmful fluids that can be picked up by storm water.