Urban Storm Water Management - Space Applications Centre Augu… · Future Storm-water Drainage Systems will be designed with a Runoff Coefficient of up to 0.95 in using Rational

GAURAV JAINCONTENT GENERATION & DISSEMINATION DIVISION (CGDD)

VEDAS RESEARCH GROUP (VRG)

EPSA

Presentation Outline

• Part - I– Urban Floods

– Types and Causes of Floods

– Effects of Urban Flooding

– Urban Storm Water Drainage Network

– Overland Flow Models for Urban Areas

– Infiltration Models

– Storm Water Routing

– Modeling Packages

– SWMM

• Part - II– SWMM Model Set-up

– Dynamic Rainfall-Runoff Simulation

– Conclusion

2Space Applications Centre ISRO

Urban Floods

• Urban floods are the floods occurring in urbanareas, and are primarily caused by heavy rainfalloverwhelming the drainage capacity.

• Urban flooding is different as compared to the flooding of

rural areas in following major aspects:

– High Impervious surface cover Increase in runoff volume and

flow velocity Reduces the time of concentration Large flows reaching discharge outlets in short time span.

– Sub-surface Drainage Network capacity of drainage network is

limited by its design involves complex open channel hydraulics; design & maintenance of drains influence capacity.

– Higher concentration of population and assets greater risk to human lives and high cost of damages to assets.

Space Applications Centre ISRO 3

Urban Floods in India

• Urban Floods in Indian Cities (2000-2010)

– 2000: Hyderabad

– 2001: Ahmedabad

– 2002: Delhi

– 2003: Delhi

– 2004: Chennai

– 2005: Severe urban floods reported in 10 cities.

Mumbai was worst affected.

– 2006: Number of affected cities rose to 22.

Surat was worst affected.

Vishakhapattanam airport inundated for over 10 days.

– 2007: Number of affected cities rose to 35.

Kolkata was worst affected.

– 2008: Jamshedpur, Mumbai, Hyderabad were worst affected.

– 2009: Delhi

– 2010: Guwahati and Delhi


Urban Flooding in Major Indian Cities


(NIUA 2016)

Guidelines for Management of Urban Flooding

National Disaster Management Authority (NDMA, 2010) of Government of India has published guidelines for management of urban flooding. The key actions recommended by the guidelines listed below:

Ministry of Urban Development will be Nodal Ministry for Urban Flooding;

Establishment of Local Network of Automatic Rainfall Gauges (ARGs) for Real-time Monitoring

with a density of 1 in every 4 sq km in all 2325 Class I, II and III cities;

Strategic Expansion of Doppler Weather Radar Network in the country to cover all Urban Areas

for enhanced Local-Scale Forecasting Capabilities with max. possible Lead-time;

Establishing Urban Flood Early Warning System;

All 2325 Class I, II and III cities and towns will be mapped on the GIS platform;

Contour Mapping will be prepared at 0.2 - 0.5 m contour interval;

Inventory of the existing storm-water drainage system will be prepared on GIS platform;

Future Storm-water Drainage Systems will be designed with a Runoff Coefficient of up to 0.95 in

using Rational Method taking into account the Approved Land-use Pattern;


Common Causes of Urban Floods in India

• Natural causes

– Heavy rainfall during monsoons;

– Storm surges in coastal cities\towns;

– Silting of water bodies and drainage channels.

• Human causes

– Population pressure and Urbanisation;

– Capacity constraint of urban drainage system;

– Faulty urban planning, and failure to consider natural hydrological system;

– Encroachment of drains;

– Unauthorized colonies (particularly in low lying areas);

– Poor water and drainage management;

– Ineffective flood control and protection measures.

– Sudden release or failure to release water from dams.

• Natural + Human causes

– the global climate change is resulting in changed weather patterns thereby

increase in high intensity rainfall events occurring for shorter periods of time;


Causes of Urban Floods


Source: Gupta, et al, 2010

Effects of Urban Flooding


• Urban flooding leads to undesirable effects such as:

Loss of life and property;

Disruptions to transport and power;

Incidences of epidemics during the monsoons;

Severe economic and infrastructure loss to industry and

commerce.

• Most vulnerable populations and elements in a city:

– Slum dwellers

– Settlements in low-lying areas

– Industrial and informal service sector workers

– Lifeline public and private infrastructure

– Ecosystems and the natural environment

Damage due to Floods in Surat City


19981998 2006

Level Area in Sq.km Level Area in Sq.km

0'-2' 5.76 0'-3' 16.04

2'-4' 6.89 3'-5' 14.55

4'-6' 4.26 5'-10' 30.03

>6' 6.32 >10' 20.82

Total 23.23 Total 81.44

YearDeaths Population

AffectedHumans Animals

1998 20 2,390 4,00,000

2006 155 4,500 19,00,000

Area Under Submergence

Damages in Floods

URBAN STORM WATER

FLOW MODELS

Hydrological and Hydraulic Processes in Urban Environment


Pervious and Impervious Surfaces

• An urban basin can be broadly considered to be made up of three types of surface:– (a) impervious areas (Aic) which are directly connected to the

drainage system, typically roads, parking lots and in some cases roofs;

– (b) additional impervious areas which are not directly connected, runoff from which flows over pervious surfaces before reaching the drainage system. Together (a) and (b) make up the total impervious area (Ai);

– (c) the remainder, pervious or semi-pervious area (Ap) consisting of lawns, gardens and parklands. The total basin area is then A = Ai + Ap

• On each surface, interception and depression storage must be satisfied before runoff commences and this storage forms an initial abstraction or initial loss from the rainfall hyetograph.


Modeling phases for urban water systems


Rainfall

Runoff

Pollutant

loading

Wash-off

Ground Water

infiltrationPipe network Wastewater inflow

Combined sewer

overflow

Treatment

worksOverland flood flows

Receiving watersURBAN DRAINAGE SYSTEM PHASES

Combined Separate

Urban Water System : Combined System


Urban Water System : Separate System


Drainage Network Design Approaches

Event Models

• designed to simulate a single

event such as the hydrograph of a

single storm;

• Examples: Rational Method

Continuous Simulation

• attempt to represent the entire

hydrologic system on computer so

as to simulate the natural system.

• maintain a continuous water

balance for the catchment so that

the conditions antecedent to each

storm event are known.

• useful for simulation of long flow

records for use in design;

evaluating the impact of change in

a catchment on stream flow;

management of storm water; and

forecasting stream flow.


ApKQ cp

36

1

ISSUES

Once in 2 Years the drains likely to saturate.

Change in land cover will saturate capacity.

ISSUES

Immense data requirement.

Requires extensive calibration & validation.

Drainage Network Design in India

• Drainage Network Design in India is based on Event Models.

• Central Public Health Engineering Organisation recommends

rational method for design of storm water drainage infrastructure in

India (CPHEEO 1993).

• It is common practice to assume the rainfall intensity corresponding

to 2 years return period for general residential areas, and 5 years

return period for important establishments and commercial areas.

• National Disaster Management Guidelines for Management of

Urban Flooding (NDMA 2010) recommends that the Storm water

Drainage Systems in Indian cities shall be designed with a runoff

coefficient of up to 0.95 in using Rational Method taking into account

the approved land-use pattern.


Storm Water Model Processes


Dynamic Rainfall-Runoff Processes in Urban Areas

Overland Flow Models for Urban Area

• LUMPED SYSTEM MODELS

1. Rainfall-intensity coefficient formulas ex. Rational Formula

2. Frequency formulas;

3. Monograph methods; and

4. Hydrograph methods.

– Models (1), (2) and (3) give magnitude of peak rate of storm runoff, but fail to provide information concerning the time of occurrence of peak runoff.

– Models (4) give information on the time distribution of runoff and hence are more useful in solving urban drainage problem.

• DISTRIBUTED SYSTEM MODELS

– Models provide not only the runoff hydrograph but also some information on the flow within the drainage area.

– Attempt to solve the continuity and momentum equations for overland flow.

– Models are computationally intensive and still largely at experimental stage.


Manning’s Overland Flow Equation

• Surface runoff occurs only when the depth of water exceeds depression storage.

• Outflow is given by following equation:

Where, – Q is runoff;

– W is width of overland flow (characteristic width);

– n is Manning’s roughness coefficient;

– d is water depth;

– dp is depth of depression (retention) storage; and

– S is slope.


Typical Values of Model ParametersSurface n

IMPERVIOUS SURFACES

Smooth asphalt 0.011

Smooth concrete 0.012

Ordinary concrete lining 0.013

Good wood 0.014

Brick with cement mortar 0.014

Vitrified clay 0.015

Cast iron 0.015

Corrugated metal pipes 0.024

Cement rubble surface 0.024

BARE SOIL

Fallow soils (no residue) 0.050

VEGETATION

Cultivated soils

Residue cover < 20% 0.060

Residue cover > 20% 0.170

Range (natural) 0.130

Grass

Short, prarie 0.150

Dense 0.240

Bermuda grass 0.410

Woods

Light underbrush 0.40

Dense underbrush 0.80


Surface Depression Storage

Impervious surfaces 0.05 - 0.10 inches

Lawns 0.10 - 0.20 inches

Pasture 0.20 inches

Forest litter 0.30 inches

Source: ASCE (1992)

Source: McCuen, R. et al. (1996)

Manning's Coefficient for Pervious and Impervious Surfaces

Depression Storage on Pervious and Impervious Surfaces

Infiltration models

• Infiltration Rate refers to the rate at which water will enter the given soil at any given time.

• Maximum rate at which a soil in any given condition is capable of absorbing water is called Infiltration Capacity.

• Infiltration capacity is affected by several factors – thickness of saturated layer and depth of surface detention, which

together induces hydrostatic pressure;

– soil moisture;

– compaction due to rain;

– washing of fines;

– compaction due to human and animal activity;

– vegetative cover; etc.

• Following methods are commonly used for modelling infiltration in urban areas:– Horton’s equation

– Green-Ampt’s model; and

– SCN Curve Number Method


Horton’s Equation

• Infiltration capacity of the soil rapidly declines

during the early part of a storm and then tends

towards a constant value after couple of hours

for the remainder of the event.

• Horton’s equation relates infiltration capacity to

initial infiltration rate (f0), and constant

infiltration (fc).

• If the rainfall intensity at the soil surface

exceeds the infiltration capacity, surface

ponding (inundation) begins, and is followed

by runoff over ground surface, once

depression storage is filled. This runoff is

called Horton’s overland flow.

• The plot of time (t) on y-axis vs. log (f - fc)

along x-axis will be a straight line.

• Decay constant can be computed as slope of

this line (typical values in between 2 to 7).


t

cc effff )( 0

fc is constant infiltrationf0 is initial infiltration rate or

maximum infiltration rateβ is a soil parameter describing the

rate of decrease of infiltration

Shallow Water Wave Equation

• One-dimensional Gradually-Varied Unsteady Flow in open channels

• Saint Venant’s equations or Shallow Water Wave equations are

approximations of the momentum and continuity equations applied

to homogenous, incompressible fluids.


CONTINUITY EQUATION: the rate of change in water depth with time in a slice of the channel is equal to the net inflow into the slice of the channel

qx

uy

t

y

)(

MOMENTUM EQUATION: the rate of change in momentum within a slice of the channel is equal to the sum of forces acting on the slice

y

u

g

qSS

x

y

x

u

g

u

t

u

gf

0

1 u is flow velocity, y is water depth,

x is the distance, t is the time

q is lateral inflow per unit length

perpendicular to the channel

g is acceleration due to gravity

S0 is the bed slope, and

Sf is the friction slope approximated using

Manning’s Equation

Local acceleration slope

Convective acceleration slope

Pressure slope

Friction slope

Assumptions

• Continuity Equation– The velocity is uniformly distributed over cross-sectional area A,

which implies that momentum coefficient, β=1;

– The pressure distribution is hydrostatic.

– The slope of the channel, S0, is constant and independent of x.

– The variation with respect to x of the internal normal stresses acting on the cross-section is relatively negligible.

– There should be no rapid change in flow cross-section or direction.

• Momentum Equation– The channel bed is non-errodable, i.e. the time rate of change of

bed profile is slow.

– The channel is straight and prismatic. Thus (dA/dx) for a given yis zero.

– Alternatively, the channel may be assumed to be sufficiently wide without rapid changes or discontinuity of width of free surface with respect to x i.e. (db/dx) is negligible.


Flow Routing

• Dynamic Equation– Complete St. Venant’s equation is solved numerically with at least (1) two

known initial conditions; and (2) two boundary conditions;

– Flow and water depth are important for detailed design of storm water infrastructure.

– For G.V.F., relationship between flow and depth not being unique, significant errors can thus be introduced if St. Venant’s Eq. are not applied.

• Kinematic Equation– Ignores backwater influences.

– Local and convective acceleration and pressure terms being small compared to the bed slope, are ignored.

– The momentum equation thus becomes Sf = S0, i.e. friction slope balances the bed slope only.

– This assumption is however valid only for overland flow or on very steep channels.

• Diffusion Wave Equation– convective and local acceleration terms in the momentum equation are

ignored.

– capable of simulating the attenuation in the flow because the pressure slope is included in the momentum equation.


Surcharged Flow in Sewer


SURCHARGES occur in a drainage system when a closed conduit becomes full and acts as conduit under pressure.

Surcharging may increase the capacity of storm water drain, but it is not desirable;

Urban Storm Water Modeling Software


Urban Storm Water Modeling Software (Contd.)


Urban Storm Water Modeling Software (Contd.)


River Engineering and Urban Drainage Research Centre (REDAC). (2012), Urban Storm water

Management Manual for Malaysia (Manual Saliran Mesra Alam Malaysia, MSMA), Pusat

Penyelidikan Kejuruteraan Sungai dan Saliran Bandar, Pulau Pinang.

Available at http://jps.penang.gov.my/index.php

http://jps.penang.gov.my/index.php

GIS Linkage of Sewer Models

Software GIS Linkage Method Vendor

SWMM Interchange U.S. EPA

CEDRA AVSand Integration CEDRA Corporation

H2OMAP Sewer/ H2OVIEW

Sewer

Interface and Integration MWH Soft

InfoWorks CS and InfoNet Interface and Integration Wallingford Software

Mouse GM and MIKE SWMM Interface DHI Water & Environment

PCSWMM GIS Integration Computational Hydraulics Int.

StormCAD and SewerCAD Interface Haestad Methods

XP-SWMM Interchange and Interface XP-Software


Integrate

GIS Software

Sewer Model

InterchangeCustom Format

GIS Format

GIS S/W SewerModel

InterfaceGIS Format

SewerModel

GIS S/W

1

2

3

SWMM Conceptual Model


SWMM’s Process ModelsSWMM’s Visual Objects

SWMM is a distributed, dynamic rainfall-runoff simulation modelused for single event or long-term (continuous) simulation of runoffquantity and quality from primarily urban areas.

Physical Objects of an Urban Drainage


Compartment Visual Objects Non-Visual Objects

Atmospheric

Compartment

1. Rain Gauge 1. Climatology (Evaporation)

2. Snow Packs

3. Time Series (temperature, evaporation, rainfall)

Land Surface

Compartment

1. Sub-catchments 1. Unit Hydrographs

2. External Inflows

3. Pollutants

4. Land Uses

Ground Water

Compartment

1. Aquifers

Transport

Compartment

1. Junction Nodes

2. Outfall Nodes

3. Flow Divider Nodes

4. Storage Units

5. Conduits

6. Pumps

7. Flow Regulators

1. Transects

2. Control Rules

3. Treatment

4. Curves (Storage, Diversion, Tidal, Pump, Rating,

Control)

5. Time Series (water stage at outfall nodes, external

inflow hydro-graphs, control settings for pumps and

flow regulators)

6. Time Patterns

SWMM5 User Interface


Flow Routing Algorithms in SWMM5

• Steady Flow: actually just adds the instantaneous sub-catchment runoff for all sub-catchments upstream of the selected channel.

– simple hydrograph translation;

– applicable only to branched networks.

• Kinematic Wave: Models Uniform, unsteady flow; No backwater, no surcharge, tree branch systems only unless flow splits are input;

– gravity force balanced by friction force;

– attenuated & delayed outflow due to channel storage;

– applicable only to branched networks.

• Dynamic Wave: Models Non-uniform, unsteady flow; Backwater, surcharge, looped or parallel sewers, street routing of flooded sewer manholes;

– solves full St. Venant equations;

– accounts for channel storage, backwater effects, pressurized flow, and reverse flow;

– applicable to any network layout;

– requires smaller time step.


Typical Applications of SWMM

• Design and sizing of drainage system components for flood control;

• Sizing of detention facilities and their appurtenances for flood control and water quality protection;

• Flood plain mapping of natural channel systems;

• Designing control strategies for minimizing combined sewer overflows;

• Evaluating the impact of inflow and infiltration on sanitary sewer overflows;

• Generating non-point source pollutant loadings for waste load allocation studies;

• Controlling site runoff using Low Impact Development practices; and

• Evaluating the effectiveness of Best Management Practices for reducing wet weather pollutant loadings.


39

Limitations of SWMM

• Not applicable to large-scale, non-urban watersheds.

• Not applicable to forested areas or irrigated cropland.

• Cannot be used with highly aggregated (e.g., daily)

rainfall data.

• Its an analysis tool, not an automated design tool.

• Not Integrated with GIS Software thereby Limited

Spatial Analysis.

Space Applications Centre ISRO

STORM WATER MODELING IN

PART OF SURAT CITY

SAC TDP/R&D Project A018


Study Area


Methodology


SHP To INP Conversion Tool


SHP To INP Conversion Tool (Contd.)


Final Plots and DEM


Land Use\ Land Cover (Actual vs. Planned)


Land Use (Actual vs. Proposed)


Land use Area in ha % of Total

Residential 1866.96 75.02

Commercial 83.47 3.35

Public and Semi-public 27.72 1.11

Public Utilities and Facilities 9.12 0.37

Recreational 97.28 3.91

Transportation 392.37 15.77

Water Body 11.76 0.47

Total 2488.68 100.00

Land Use Area in ha % of Total

Agriculture Crop Land 308.21 12.38

Agriculture Fallow Land 474.33 19.06

Built-up Residential\ Commercial\ Public and Semi-

public\ Mixed-use\ Industrial etc.

1127.59 45.31

Built-up Transportation (Roads and Rail) 230.17 9.25

Built-up Vacant Land\ Wasteland\ Vegetated Area etc. 289.49 11.63

Water Body River\ Canal\ Drains etc. 58.89 2.37

Total 2488.68 100.00

actual

proposed

55%Actual Developed Area

Soil Sampling


Series

Number

Description

82 Very deep, moderately well drained soil,

calcareous, fine soils of nearly level

alluvial plain with slight erosion and slight

salinity, associated with very deep, well

drained, calcareous, fine soils on very

gently sloping lands, with slight erosion

and slight salinity.

136 Very deep, moderately well drained,

calcareous, very fine soils of nearly level

plain with slight erosion, and slight

salinity.

140 Very deep, moderately well drained,

calcareous, very fine soils of nearly level

plain, with slight erosion, and moderate

salinity.

Parameter Value

Max. Infiltration Rate 50 mm/hr

Min. Infiltration Rate 2 mm/hr

Decay Constant 7.0

Drying Time 10 days

Max. Infiltration Volume 0

Recommended Infiltration Parameters

Horton’s Infiltration Model


Site

ID

Max. Infiltration

Rate in cm/hr

Min. Infiltration

Rate in cm/hr

K (Decay

Constant)

1 14.40 0.17 13.8739

2 7.20 0.20 14.8255

3 10.80 0.20 14.0621

4 12.00 0.13 10.0243

5 6.00 0.24 17.8932

6 10.80 0.15 11.4436

7 12.00 0.10 7.2282

8 4.80 0.24 17.0928

9 10.80 0.08 5.2320

10 7.20 0.20 15.0959

11 18.00 0.12 9.3990

12 10.80 0.10 7.3809

13 9.60 0.12 8.6158

14 8.40 0.12 8.2930

15 12.00 0.13 9.8311

16 8.40 0.20 15.2105

17 21.60 0.07 4.2286

18 6.00 0.15 10.7010

19 9.60 0.15 11.0519

20 18.00 0.12 9.3108

0

20

40

60

80

100

120

0.000 0.200 0.400 0.600 0.800 1.000 1.200 1.400

Infi

ltra

tio

n r

ate

(mm

/hr)

Time(hr)

0

0.5

1

1.5

2

2.5

0.000 0.500 1.000 1.500

log(

f-fc

)

Time(hr)

Sub-catchment Area

• An urban drainage basin is sub-divided into large number of sub-

catchment areas.

• A SUB-CATCHMENT AREA is a hydrological unit, whose

topography and drainage system elements direct the surface runoff

to a single discharge point.

• This discharge outlet point may be a node of drainage network or

any other sub-catchment.


Pervious Surface

Impervious Surface without Depression Storage

Impervious Surface with Depression Storage

IMPERVIOUS AND PERVIOUS SUB-AREA

Delineation of Sub-catchments


(a) (b) (c) (d)

Sub-catchment with Impervious Area


Pervious and Impervious Land Cover


Characteristic Width

• SWMM recommends that an initial estimate of characteristic width of the

overland flow path for sheet flow runoff may be taken as ratio of sub-

catchment area, to the average maximum overland flow length.

• The maximum overland flow length is the length of the flow path from

farthest drainage point of the sub-catchment before the flow becomes

channelized.

• The maximum lengths from several different possible flow paths should be

averaged to compute characteristic width.


Characteristic Width and Slope


Drainage Network Layouts and Outfalls


Storm Water Drainage Network


Shape-files Converted to INP File


Climate and Tide Data


200

250

300

350

400

0

10

20

30

40

50

Cu

mu

lati

ve R

ain

fall

(mm

)

Ho

url

y R

ain

fall

(mm

)

Date ( Year 2012)

Hourly Rainfall (mm)

Cumulative Rainfall (mm)

TIDAL STAGE

RAINFALL

Month Jan Feb Mar Apr May Jun

(mm/day) 5.0 7.0 8.0 9.0 11.0 9.0

Month Jul Aug Sep Oct Nov Dec

(mm/day) 5.0 5.0 5.0 5.0 5.0 4.0

Month-wise Mean Daily Evaporation

EVAPORATION

Continuity Errors


Runoff Quantity Continuity Volume (ha-m) Depth (mm)

Total Precipitation 293.659 118.000

Evaporation Loss 23.449 9.422

Infiltration Loss 59.149 23.768

Surface Runoff 212.770 85.497

Final Surface Storage 0.780 0.313

Continuity Error (%) -0.848 OK

Flow Routing Continuity Volume (ha-m) Volume (10-6 Liters)

Dry Weather Inflow 0.000 0.000

Wet Weather Inflow 73.137 731.380

External Inflow 0.258 2.585

External Outflow 65.626 656.262

Internal Outflow 7.748 77.479

Initial Stored Volume 0.000 0.001

Final Stored Volume 0.054 0.538

Continuity Error (%) -0.043 OK

7.9%

20.0%

71.8%

0.3%Volume (ha-m)

Evaporation Loss

Infiltration Loss

Surface Runoff

Final Surface Storage

89.4%

10.6%

0.1% Volume (ha-m)

External Outflow

Internal Outflow

Final Stored Volume

1 ha-m = 104 cu. m = 10 Million Liter

34.37%

Inflow and Depth of Runoff at Outfalls


Out-

fall ID

Outfall

Node

ID

Average

Flow

(CMS)

Max.

Flow

(CMS)

Total

Volume

(ML)

1 OUT1 0.045 0.379 2.928

2 OUT2 0.058 0.435 3.707

OUT10 0.610 2.900 38.987

3 OUT3 1.050 9.094 69.322

4 OUT4 0.396 3.379 25.987

OUT11 0.219 1.975 14.052

5 OUT5 0.268 1.656 17.714

6 OUT6 0.803 5.303 54.644

OUT12 1.156 9.824 76.488

7 OUT7 0.318 1.787 20.606

8 OUT8 0.588 4.396 42.162

OUT13 1.019 5.683 73.818

9 OUT9 0.771 4.715 43.208

OUT14 1.521 8.546 96.377

10 OUT15 1.198 7.024 78.843

System 10.026 65.717 658.852

Surface Runoff


Estimated Runoff Coefficient


Runoff Coefficient Variation with

Impervious Land Cover


0 10 20 30 40 50 60 70 80 90 100

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

f(x) = 0.0036114x + 0.5409395R² = 0.9690885

Percent Impervious vs. Runoff Coefficient

Percent Impervious

Runoff

Coeff

icie

nt

Node Water Depth and Inflow


Surcharge and Flooding at Nodes


Magnitude & Time of Occurrence of Flood


Link Flow and Velocity


Dynamic Rainfall Runoff Simulation


Problematic Areas (SMC)

Access to Storm Water Drainage


1462:Sub-catchments topologically overlapping with SWD line;

1724:Adjoining Sub-catchments topologically touching above sub-catchments;

3186:Total Sub-catchments with access to SWD;1091.16 ha area (43.84 % of total and 67.5 % of developed area)

1061:Sub-catchments connected to S.W. node (400)

and adjacent sub-

catchments (661);

1195:Sub-catchments indirectly connected above sub-catchments;

2256:Total Sub-catchments with access to SWD;755.65 ha area (30.37% of total and 55.65% of developed area)

Flood Risk Assessment


0

50

100

150

0 1 2

Ra

infa

ll i

n m

m

Time in Hours

2 Year ReturnPeriod

5 Year ReturnPeriod

50 Year ReturnPeriod

Runoff Quantity

Continuity

Scenario (Frequency)

2 Year 5 Year 50 Year

Precipitation (mm) 45.00 70.00 100.00

Precipitation (ha-m) 111.99 174.20 248.86

Evaporation Loss (ha-m) 3.78 3.81 3.83

Infiltration (ha-m) 18.24 18.42 18.54

Surface Runoff (ha-m) 93.41 156.11 232.44

Continuity Error (%) -3.07 -2.38 -2.39

Number of NodesHours Flooded 2

Year5

Year50

Year< 15 minutes 73 103 109

15 – 30 minutes 8 13 1630 – 45 minutes 13 17 2045 – 60 minutes 17 17 33

> 60 minutes 6 26 42Total 117 176 220

Conclusion

• Continuous Simulation Models have potential for

– evaluating drainage network designs;

– identifying areas vulnerable to urban flooding;

– managing of storm water (LID, Rain Water Harvesting etc);

– providing early warning of urban floods; and

– assessing impact of land gradation and concretisation.

• this study demonstrated the application of high

spatial resolution satellite data and digital elevation

models for retrieval of surface parameters for

modelling storm water flow in urban areas.

• the study provides possible application for future

very high resolution satellite data and ALTM.



Documents

Urban Storm Water Management - Space Applications Centre Augu… · Future Storm-water Drainage Systems will be designed with a Runoff Coefficient of up to 0.95 in using Rational