URP 317: Site and Area Planning
SESSION #
STORM WATER MANAGEMENT IN SITE
PLANNING
SOURAV DAS
LECTURER
DEPARTMENT OF URBAN AND REGIONAL PLANNING, CUET
WHAT IS STROM WATER MANAGEMENT
Storm water management and sewerage disposal is
selected for site which are related to hydrologic cycle
Storm drainage takes off the flow of surface water
Substitute of natural drainage
Unnecessary for the low density area ( 2 family per acre)
Doesn’t require continuous system but need to discharge
water in to the local lake, canal or streams
Separate from the sewage disposal system
STROM WATER MANAGEMENT IN CTG
• Chittagong is located in the tropical zone, where high
temperature and heavy rainfall with high humidity is a general
characteristic of the summer season.
• Annual rainfall in the city fluctuates between 2100mm and
3800mm, of which 2400mm occurs only during the monsoon.
• However, such climate has been there for centuries, while water
logging is a comparatively recent phenomenon.
• In the last decade or so, this problem has been increasing due to
population growth, economic agglomeration with unplanned
urbanisation, illegal refilling of natural water channels, and
encroachment of drains.
STROM WATER MANAGEMENT IN CTG
• Several authoritative bodies are responsible for managing the drainage
system of the city.
• The core responsibility for storm water drainage and sewerage belongs
to CWASA.
• However, CWASA has neither developed any sewerage system nor storm
water drainage infrastructure till date.
• CCC is mainly working on the local and tertiary drainage development
and construction and is also responsible to keep the drains clean.
• CDA's role is to incorporate drains in land-use and structural plans and
allot space in city designs.
• The Bangladesh Water Development Board (BWDB), another statutory
body, is responsible to plan the flood management of CCC and they are
both involved in linking embankment with the drainage system.
STROM WATER MANAGEMENT IN CTG
• The Chittagong Storm Water Drainage and Flood Control
Master Plan 1995 proposed for developing the drainage
system in five phases within the plan period of 1995-2015.
• No progress is noticed in the reclamation of the Chaktai
canal, the backbone of drainage system of the port city,
either.
• There has to be one central authority under which CDA,
WASA and other bodies can work together, towards the same
goal.
• Such mechanisms can only be implemented with collective,
coordinated efforts under a city government arrangement.
PRINCIPLES OF STORMWATER DRAINAGE PLAN
The principles set forth in the NWMP, and based on the practical
experiences in other growing urban areas. The final detailed
drainage layout plan should be prepared based on the following
principles:
• Detention-based gravity drainage; temporary pumping only
during extreme floods.
• Separate systems for stormwater and domestic wastewater
drainage.
• Operation and maintenance embedded in the activities of the
local government; adequate funds in the annual budget.
WHY STROM WATER MANAGEMENT
Traditional way, collecting storm water in piped network
and transporting off site as quickly as possible
Water was considered as a problem
Storm Water runoff brings pollutants once they run
over disturbed land, through the debris, chemicals of
the streets, fertilizer and insecticides of the field.
Large storm discharges must be controlled or treated
before disposed to the river, lake
Due to site work, characteristics and irregularities
removed from the site
WHY STROM WATER MANAGEMENT
Volume and velocity of the storm water runoff increases
Rainfall and runoff no longer deflected and cannot infiltrate into the
compacted soil
Increase of impervious area decrease the environmental quality
10-15% imperviousness decreases the habitat quality
Falling groundwater tables, dry streams, degraded surface quality
Interception
WHY STROM WATER MANAGEMENT
WHY STROM WATER MANAGEMENT
Development and environmental protection can co-exist
A general rethinking has developed toward “green
infrastructure” / “low impact design” (LID)
Goal is to design a hydrologically functional site that
mimics pre-development conditions
Water is considered as resources than a problem
Interaction with the environment is carefully weighed to
maximize total benefits and minimize cost
Strategies: vegetated swales, infiltration structures,
rain gardens, retention and detention basin and green
roofs
GREEN INFRASTRUCTURE
GREEN INFRASTRUCTURE
Green infrastructure integrates natural services such as --
• Infiltration
• Micro-biotic activity in soils
• The diversity of stable ecosystems
• The implications of site development to create a win-
win situation.
GREEN INFRASTRUCTURE
GREEN INFRASTRUCTURE
WHY STROM WATER MANAGEMENT
Benefits of a green infrastructure ------
Increased infiltration and groundwater recharge
Decreased pollution loads on surface water
Increased biodiversity
Reduction in the heat island effects of development
Improved air quality
GREEN CITY CONCEPT
COMPUTATION OF PIPE SIZE
Required pipe size is depends on the
- slope, area being drained, the coefficient of runoff, intensity of
the storm at the time of peak flow
Relational method used to estimate the peak runoff
Q= CiA
Where, Q= discharge in cubic feet per second (cfs)
C= runoff co-efficient (Fraction of total rainfall that runs off on the
surface rather than penetrating the ground )
i= intensity
A= Area drained
This information is required to estimate the pipe size as well as
cost estimation for the site
STRATEGIES OF STORM WATER MANAGEMENT
1. Bio-retention Swale
2. Pervious Pavement Shoulder
3. Environmentally Friendly Concrete
4. Preserved Forest Buffer
5. Restored and Stormwater Wetlands
6. Stream Restoration
7. Wildlife Crossing
8. Soil Amendments
STRATEGIES OF STORM WATER MANAGEMENT
Vegetative swales
Shallow grass-covered hydraulic conveyance
channels
Help to slow runoff, filter water and facilitate
infiltration.
Suitability depends on land use, soil type, slope,
imperviousness of the contributing watershed, and
dimensions and slope of the grassed swale system.
Watersheds are areas of land that drain water,
sediment and dissolved materials to a common
receiving body or outlet, and they are critical to
environmental, financial, and social health.
Regardless of a watershed's size (they can range
from a few acres to thousands of square miles),
Can be used to manage runoff from drainage areas
less than 10 acres in size, with slopes no greater
than 5 percent.
Use of swales decrease the site development cost
than pipe system
Easy to maintain
STRATEGIES OF STORM WATER MANAGEMENT
Infiltration and recharge
Preferred method of storm water quality management
Infiltration can be used for pollutant removal, but provide only
limited cleansing.
Infiltration removes particulates and pollutants that might attach
to soil particles, but water soluble pollutants such as nutrients,
pesticides, or salts travel through the soil medium dissolved in the
water
When water soluble pollutants are risky, the design must provide
for a biological treatment
Loss of ground water recharge can be reduced by infiltration
Soil texture is an important element in determining infiltration
rates.
STRATEGIES OF STORM WATER MANAGEMENT
Detention and Retention Basins
Detention basins are usually dry basins that only fill with water
during a rain.
They work by delaying the storm water
Effectiveness of a Detention basin depends on the drainage area in
which it operates and the location of the basin in the watershed
The lower the basin is in a watershed, the less effective it is in
providing a positive or beneficial effect.
Detention basins may be designed to meet a pre-development
storm rate of discharge
Site designers must study existing drainage patterns and pathways
to identify opportunities that exist on the site.
STRATEGIES OF STORM WATER MANAGEMENT
Detention and retention basins
Minimum drainage area for a wet pond is 10 acres
The drainage area should be adjusted according to the
Rainfall characteristics of the area
The amount of anticipated runoff
The type of land use
Pond geometry and depth
The settling rate of the expected particulates
STRATEGIES OF STORM WATER MANAGEMENT
Detention and Retention Basins
Alternative of infiltration and recharge system
It holds the water in a pool
The retention basin loses water through infiltration and
evaporation
The design of wet ponds should be done by professionals to
balance with the site constraints
It is generally a balancing act between cost, site issues (such as
slope or drainage area), appearance, and pond function.
Advantages of a wet pond
- effective process for the removal of certain urban pollutants
through settling in the permanent pool.
DETENTION AND RETENTION BASINS
STRATEGIES OF STORM WATER MANAGEMENT
Vegetated roofs
Vegetated roof covers, or “green roofs,” provide an important
strategy for the management of storm water.
Green roofs consist of an impermeable roof membrane overlaid
with a lightweight planting mix with a high infiltration rate and
vegetated with plants tolerant of heat, and periodic inundations.
Common flat roofs can be designed to reduce runoff by increasing
the roughness of the roof surface or by restricting roof drains.
Such installations can significantly reduce runoff volumes and in
turn reduce development costs.
In older cities the installation of roof top systems can contribute to
reducing the costs of rehabilitating infrastructure
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