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1
Urban Hydrology and Drainage Systems
Tawatchai Tingsanchali, D.EngAdjunct Professor,
Asian Institute of Technology
Pathumthani, Thailand
Professional Development Training Program for SriLanka Land Reclamation and Development Corporation
Urban Flood Management and Disaster RiskManagement
24 March - 4 April, 2014
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Hydrologic cycle
Source: U.S. Global Change Research Program (USGCRP))
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Hydrologic cycle
Water falls to the ground as rain, snow, hail, sleet
etc. from clouds
Water infiltrates or seeps into the ground, a process
called percolation
Subsurface water
I. taken up by the vegetation and returns to
the atmosphere through transpiration, or
evaporation of water from all surfaces
II. Enter to water bodies as spring water/
groundwater.
Excess water runs over the ground surface as runoff
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Interception
leaves and stems of vegetation, buildings, etc
capture some of the precipitation
intercepted water is dissipated byevaporation
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Evapotranspiration
Evaporation from land surface
includes direct evaporative loss from the soil
surface, depression storages and intercepted
water
Transpiration from vegetation
Depends on heat energy, wind, moisture
availability
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Infiltration The process of penetrating of water from the
ground surface into the soil
Infiltration rate depends on
condition of soil surface, existing land cover,
properties of soil beneath.
porosity, hydraulic conductivity and existing moisturecontent of the soil.
infiltration vary with time and space
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Infiltration & percolation
Infiltration
Percolation
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Surface water flow
excess over infiltration
releases from houses, industries and irrigation
discharge from springs
secretion (or exfiltration) from saturated and
unsaturated soil as base flow
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Runoff generation from rainfall
As the rainfall continues, the rainfall intensity
exceeds the infiltration rate
excess water begins to pond , fill depressions
and potholes on the ground surface
After that overland flow starts
overland flow concentrates into rill flow, then
into gully flow and continues in the
catchment slope to discharge into a stream
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Impacts of urbanization
Urban areas- high population density , more commercial
activities
- Residents have an advantages over ruralsettlements
- Lower specific costs for services
- larger and concentrated customer base
- Access to all services
- More opportunities
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Impacts of urbanization on hydrology
In developed areas, Removal of vegetation reduce interception
Infrastructure (asphalt roads, concrete
structures) increase impervious area andprevent water from infiltrating into the soil.
Runoff coefficient increases.
More stormwater runoff
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Impacts of urbanization on hydrology
In developed areas,
Efficient and faster hydraulic conveyance
systems
supply of large volumes of pipe water to
generate more drainage water/ wastewater
increase of discharging pollutants to natural
water bodies
Urbanization More stormwater runoff
Poor water quality
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Effect of urbanization on runoff
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Increased peak discharge of runoff Increased volume of runoff
Reduced time of concentration
Reduced base flow from the catchment
Increased wastewater flow/drainage flow
Impacts of urbanization on hydrology
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Increased frequency and severity of offsitedownstream flooding
Reduced stream flow and lower water table
levels during dry weather Loss of wetlands
Increase in flow velocity
increased land erosionincreased stream channel erosion
Impacts of urbanization on hydrology
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pollution significantly degrade water qualityand aquatic habitat.
Poor water quality during dry weather flow
Urbanization increases the amount ofpollutants in storm runoff
pollutants and suspended matter in the stormchange the nature of the substrate in receiving
body.
Habitats of aquatic life are threatened ,biodiversity is affected.
Impacts of urbanization on hydrology
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Buildings, pavements, etc. have high thermalbulk properties and surface radiative
properties
provide multiple surfaces for reflection and
absorption of sunlight
waste heat from automobiles, airconditioning, industry roofs
surface temperature and overall ambient air
temperature in an urban area to rise.
Impacts of urbanization
Urban heat build-up and rainfall changes
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Mitigation of adverse impacts of
urbanization
Requires a multi-disciplinary approach throughstructural and non-structural measures.
The civil engineering components fall mainly to
the structural measures Non-structural measures do not involve
constructions, policies and legislations
Preventive actions for hydrological impacts arealways simpler and cost effective compared tocorrective actions.
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Non structural measures
provisions for floodplain zoning and regulation
to regulate land use changes
some areas are left out for flood control
Introduction of legislations for
imposing mandatory storm water retention or
detention facility within the premises.
Building codes to include stormwater storage facilities
provisions for flood-proofing of buildingsBuildings are required to adopt flood proofing
techniques to coop with floods
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Non structural measures
Legislations
To control water pollution by imposing quality
standards for wastewater and solid waste disposals in
urban environments
To improve the quality at the premises itself byowners before releasing to public facilities such as
stormwater drains
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Flow detention and retardation structures
storage type
detention ponds
retarding basins
off-site storage structures
infiltration type
pervious pavements
infiltration trenches
Infiltration ponds and inlets
Structural measures
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Detention ponds & Retention ponds
Detention pond
Retention pond
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Retention ponds
Retention pond is a reservoir to provide aresidence time
to retain water and regulate outflow
to settle down pollutants and sediments
Capacity is based on the runoff generated fromthe area
A dead storage is provided to trap heavy metal
pollutants and sediments Sluices and spillways are provided to discharge
the excess water
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Detention ponds
ponds provided in residential and commercialplots
to collect excess water during a storm and to
release gradually by a controlled outlet
stormwater release is regulated to reduce the
flood peak downstream.
open areas such as play grounds and parks are
used as on-site detention ponds.Once the water is completely released the facility
is cleaned and put into normal use.
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Pervious pavements
Pervious pavements are permeable surfaceswhere the runoff can pass and infiltrate into theground.
Pervious pavements facilitate
peak flow reductionground recharge
pollution filtering.
types:
i) porous asphalt pavements
ii) porous concrete pavements
iii) garden blocks
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Infiltration ponds
Infiltration ponds are similar to detentionponds but they are specifically provided to
infiltrate the routed stormwater
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Infiltration inlets
Infiltration inlets are draining structures thatreplace the gulley holes, or the uptake points
for conventional storm water
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Types of sewer systems
Principles of collection:
Combined
Separate
Above ground/underground
Principles of transport
Gravity
Pressure
Vacuum
2
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Wetlands
Wetlands are shallow ponds with growing aquatic
plants constructed across streams at depressionsfor removal of pollutants in water
They provide a detention time for the water to
settle pollutants/sediments and for the aquaticplants to uptake pollutants.
(Source Ascuntar Rias et al., 2009) (Source Rich Axler et al., 2008)
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Flood proofing
Flood proofing is the use of permanent,contingent or emergency techniques to
prevent flood waters from reaching buildings
and infrastructure facilities
Flood proofing
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Flood proofing
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Urban catchment modeling concepts
Simulation of hydrological processes of theurban catchment
to derive runoff required for the design ofappropriate stormwater drainage system.
Event-based hydrologic modeling is carried out toestimate flows due to a given storm event
useful for deciding design flows of systemcomponents
Continuous hydrologic modeling is carried out toderive long-term continuous flows
useful in water quality estimations in the system
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Types of catchment models
Hydrologic Models
DeterministicStochastic
Physically basedConceptualDistributedLumped
T f h d l
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Stochastic models
Statistical concepts are used to link input to the
model output
Deterministic models
Determines an output for a given input based
on certain formulation
Types of catchment models
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REFERENCES
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Vongvisessomjai, N., Tingsanchali, T. and Babel, M.S. (2009), Non-
deposition Design Criteria for Sewers with Part-full flow, UUrban WaterU,
Vol.7, Issue 1, pp. 61-77, Taylor and Francis, U.K.
REFERENCES
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THANK YOU