Storm Water Flood Modeling in Urban Areas

Dr. Y.R. Satyaji Rao Scientist ’F’ and Head Deltaic Regional Centre National Institute of Hydrology Kakinada, A.P [email protected] Why Storm Water Flood Modeling ?

To design effective storm water drains to avoid flooding or to identify flood prone areas in new urban areas

To understand system inflow and outflow characteristics in new and existing urban areas

To understand storm water network efficiencies in existing urban areas.

To propose or incorporate various flood mitigation measures in existing urban areas Urban flooding It is triggered when surface runoff exceeds the capacity of drainage systems, which happens when heavy rainfall pours on sewers with the limited capacity, or even medium rainfall falls on poorly planned or operated drainage systems (Kamal and Rabbi, 1998; Arambepola, 2002). Definition of Urban Drainage Systems

Urban drainage systems are defined as physical facilities that collect, store, convey, and treat runoff in urban areas. These facilities normally include detention and retention facilities, streets, storm sewers, inlets, open channels, and special structures such as inlets, manholes, and energy dissipaters” (ASCE and WEF, 1992). Popular Storm Water Model Software Packages

 US EPA (SWMM)

 DHI (MIKE URBAN)

 Bentley (Storm net)

  Wallingford

 XPSWMM XP Software Inc. SELECTED MODEL

XP SWMM/EPA SWMM (Stormwater and Wastewater Management Model)

XPSWMM used to develop link-node and spatially distributed models that are used for the analysis, design and simulation of storm and waste water system. It also models flow and pollutant in natural system including rivers, lakes, and floodplains with groundwater interaction. What Is SWMM?

SWMM is a distributed dynamic rainfall-runoff simulation model used for single event or long-term (continuous) simulation of runoff quantity and quality from primarily urban areas. SWMM’s Process Models Hydrologic Modeling Features

• Spatially and time varying rainfall • Evaporation of standing surface water • Snow accumulation and melting • Interception from depression storage • Infiltration into soil layers • Percolation into shallow groundwater • Interflow between groundwater & channels • Nonlinear routing of overland flow Hydraulic Modeling Features

• Handles drainage networks of any size • Accommodates various conduit shapes as well as irregular natural channels • Model component consists of pumps, regulators, storage units etc. • Allows external inflows from runoff, groundwater, RDII, (Rainfall Derived Infiltration or Inflow) sanitary, DWF (Dry weather Flow), and user-supplied time series input • Uses flexible rule-based controls for pumps and regulators • Models various flow regimes, such as backwater, surcharging, reverse flow, and surface ponding Water Quality Modeling Features

• Pollutant buildup over different land uses • Pollutant washoff during runoff events • Reduction in buildup from street cleaning • Inflows from user-defined sources and sanitary DWF • WQ routing through the drainage network • User-defined treatment functions Typical Applications of SWMM

• Design and sizing of drainage system components including detention facilities • Flood plain mapping of natural channel systems • Control of combined and sanitary sewer overflows • Generating non-point source pollutant loadings for wasteload allocation studies • Evaluating BMPs 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 Process of Storm to Sewer network

Storm

Hydrological model Catchment

Sewer Hydraulic model Design of Storm sewer system

Design storms are routinely used for designing storm sewer system.

A design storm is a hypothetical storm with specific duration D and return period T.

The information of design storms is conveniently presented in the form of depth-duration-frequency (DDF) curves or intensity-duration-frequency (IDF) curves. Modeling of Storm Sewer System

Rainfall

Losses model

Effective rainfall

SCS/Unit hydrograph Inflow hydrograph of the inlet Non-steady flow hydraulics numerical solutions Outflow hydrograph of sewer system BASE MAP PHASE DERIVED MAP PHASE

SUB_BASIN AREA

ELEV SLOPE

SOILS INFIL

HOUSES RUNOFF MODEL INPUT

DRIVEWAYS

CUL-DE-SACS IMPERV

ROADS

DRAIN NET GUTTER LENGTH

CANALS Procedure for GIS to SWMM ITERPRETIVE PHASE FINAL PHASE

SUB_BASIN Q1

Point Discharge SUB_BASIN l RUNOFF MODEL INPUT SUB_BASIN Ql TOTAL PEAK DISCHARGE

DRAIN GUTTER LENGTH Note: for each sub basin in

SUB_BASIN Qn Procedure for GIS to SWMM SWMM Model Structure Two Case Studies: Patna and Chennai Chennai Floods The last century records on catastrophic flooding in Chennai

1946 (Chembarambakkam tank surplused into Adayar river with a discharge 20,000 Cusecs)

1976 (Heavy flood at Adayar-Kotturpuram)

1985 (Floods in Adayar River and discharge 63,000 Cusec)

1996 (Karanodal bridge collapsed)

1998 (Madvaram surplus water )

2005 (100 yr recurring rainfall of 40 cm in a day caused heavy inundation in and around Chennai city) Main reasons for these floods caused by heavy rain associated by cyclonic activity and failure of major rivers and other drainage systems. ….Chennai Floods

• Late Thiru A.R. Venkatachari, who was a special Superintending Engineer, investigated Madras floods of 1943 and suggested to adopt a value of 1000 for “C” in the Ryve’s formula for calculating flood discharge for tanks. This suggestion has not been actively pursued and almost all the tanks of the surplus weirs were designed for a “C” value of only 500. It was concluded that this is one of the major reasons for the beach of the tanks. ..Chennai Floods

• Mott MacDonald International, Cambridge, UK in the year 1993, studied three cases of catastrophic flooding in Madras in the 20th century occurred in 1943, 1976 and 1985. It was concluded that heavy rains associated with cyclonic activity caused these floods and these events were all attributed to failure of the major river drainage systems. In addition to these, it was also mentioned that flooding of a less catastrophic nature occurs regularly in low-lying areas of the city where the local drainage infrastructure is inadequate or inoperative. ..Chennai Floods

• Thereafter, there is no scientific study has been conducted on urban hydrology of Chennai city (using 15 minute rainfall and 0.25 m topographical details). However, comprehensive developmental activities related to micro/macro drainage system in Chennai Metropolitan city has been proposed by Chennai Metropolitan Development Authority (CMDA) in the second master plan of Chennai metropolitan city up to 2026 (www.cmdachennai.org). ..Chennai Floods • Recently, Chennai Corporation has taken up the project aiming at creating economically productive, efficient, equitable and responsive cities especially on comprehensive storm water management facilities for Chennai Corporation under JNNURM. • Among various needs, the storm water drainage for urban areas is becoming a problem and is highly complicated. Therefore, it is high time to review and redesign the storm water drainage systems to find out engineering solutions. • M/s Aarvee Associates, Hyderabad have been hired to conduct topographical surveys, and mapping existing storm water drains/roads along with C/S details. Project Objectives:

1. Evaluation of existing storm water drainage network efficiency in the study area

2. To find out the inflow-outflow hydrograph at various outlets and the water surface profile along the storm water drains.

3. Feasibility of improvement of the existing storm water drainage network or to propose additional network to mitigate urban storm water flooding in the study area.

4. Dissemination of results of the project through workshops/ brain storming sessions/awareness programs with the help of NGO’s/Govt., departments/Academic Institutions in the study area and elsewhere. Project Location

Tamilnadu

Chennai Corporation with sub watersheds Otteri nullah sub basin Otteri nullah watershed ….Project Area Total Length: 10.0 km Watershed area: 30 sqkm

Nungambakkam Rain Gauge Station (IMD)

Average Annual Rainfall: 1300 mm Highest daily rainfall 40 cm (2005) Highest hourly rainfall 93.5 mm (1996)

Delineation of Watersheds in Chennai Corporation Instrumentation in Project Location: Monitoring Network of Rain gauges and Water level Recorders Application of Model (XP-SWMM)

Schematization of Project Area: Micro watersheds(86), Node (121) and Links (120) Delineated micro watersheds of the study area in XP-SWMM Connectivity of micro watersheds with nodes in XP-SWMM Details of links considered in the XP-SWMM Model Testing

6.5 0 7.0 0 6.0 6.5 10 20 6.0 5.5 40 20 5.5 5.0 60 Stage(m) Stage(m) 5.0 Rainfall (mm) 30 Rainfall(mm) 4.5 4.5 80 4.0 40 4.0 100 1 6 11 16 21 1 6 11 16 21 Time(hr) Time(hr) Rainfall Model Observed Rainfall model Observed

Comparison between observed and modeled Comparison between observed and modeled stage at Anna Nagar (25th Oct. 2011) stage at Anna Nagar (4th Nov. 2011) Rainfall Modeled Observed

0 6.9 5 6.4 10 5.9 15

Stage (m) Stage 5.4 20 4.9 25 (mm/hr) Intensity Rainfall

4.4 30 1 9 17 25 33 41 49 Time (hr)

Comparison between observed and simulated stage at Anna Nagar (25-10-2011, 9.00 to 27-10-2011, 12.00 hrs)

5.6 R2 = 0.8469 5.4

5.2

5.0

4.8 Observed (Stage in m) in (Stage Observed

4.6

4.4 Correlation between observed and 4.4 4.6 4.8 5 5.2 5.4 5.6 simulated stage at Anna Nagar Modeled (Stage in m) Rainfall Modeled Observed 1 0 5 0.8 10 0.6 15 20 0.4 25 Stage Stage (m) 30 0.2 35

0 40 IntensityRainfall (mm/hr) 1 9 17 25 33 41 49 Time (hr)

Comparison between observed and simulated stage at Basin Bridge (25-10-2011, 9.00 to 27-10-2011, 12.00 hrs)

0.5 R2 = 0.837 0.4

0.3

0.2

Observed (Stage in m)in (Stage Observed 0.1

0.0 Correlation between observed and 0 0.1 0.2 0.3 0.4 0.5 Modeled (Stage in m ) simulated stage at Basin Bridge 2 yr 5 yr 10 yr 25 yr 100

40 Rainfall(mm)

0 1 3 5 7 9 11 13 15 17 19 21 23

Time (hr)

24 hr Design Storms for various Return Periods Details of water balance, flood peaks with existing and proposed longitudinal profile of Otteri Nullah against various return period of design storm

24 hr System System Peak (m3/s)  % Error design Inflow (m3) Outflow (m3) storm return period Existing Proposed Existing Proposed Existing Proposed Existing Proposed

2 27.57 53.00 2.7463*106 2.7463*106 2.7429*106 2.7538*106 0.065 -0.323

5 33.80 61.40 4.6879*106 4.6879*106 4.6817*106 4.6931*106 0.065 -0.110

10 37.58 69.31 5.9395*106 5.9395*106 5.9345*106 5.9411*106 0.031 -0.050

25 42.37 75.60 7.6090*106 7.6091*106 7.6056*106 7.6092*106 0.005 -0.001 80 0 70 20 40 60 60 50 80 40 100 30 120 140 Rainfall (mm/hr) Rainfall

Discharge Discharge (Cumec) 20 160 10 180 0 200 0 4 8 12 16 20 24 28 32 36 Time (hr)

2 Yr 5 Yr 10 Yr 25 Yr

24hr design hyetographs and its corresponding hydrographs at sub basin outfall with existing longitudinal Profile Flood Mitigation Measures 80 0

70 20 40 60 60 50 80 40 100

30 120 Rainfall(mm/hr)

Discharge(Cumec) 140 20 160 10 180 0 200 0 4 8 12 16 20 24 28 32 36 Time (hr)

2 Yr 5 Yr 10 Yr 25 Yr

24hr design hyetographs and its corresponding hydrographs at sub basin outfall with proposed longitudinal profile. A A. Plan view of flooding nodes in the study area for 2 yrs return period design storm with existing L/P B B. Proposed L/P Water surface profile in the OND with 2-yr return period 24 - hrs design storm with/with out boundary conditions

Water Surface Profile Water Surface Profile Plan View Plan View Impact of Flood Mitigation Measures at Node Points

Total SWD Nodes (92) Total OND Nodes (29) 24-hrs 24-hrs FN FN FN FN storm storm Existing Proposed Existing Proposed Return Return L/P L/P period L/P period L/P

2 Yr 64 54 2 Yr 5 1

5 Yr 68 58 5 Yr 6 4

25 Yr 71 61 25 Yr 6 4

100 Yr 71 71 100 Yr 6 6 Location of proposed diversion channel by PWD in the study area Two years return period of hyetograph and corresponding hydrograph at Anna Nagar with and without diversion channel

Rainfall With Diversion Channel Without Diversion Channel

12 0

10 10

8 20

6 30

4 40 (mm) Rainfall Discharge(Cumec) 2 50

0 60 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Time (hours) Existing Stormwater drainage conditions in the study area

Objectives Conclusions

Evaluation of existing storm water The present storm drainage network is drainage network efficiency in the study not sufficient even for two year return area period rainfall except ON drain.

To find out the inflow-outflow Inflow/out flow Hydrographs and water hydrograph at various outlets and the surface profiles were developed at all water surface profile along the storm nodes in the project area after testing of water drains. the XP-SWMM model. Flood hydrographs have been developed at basin out let with tide and without tide for 2,5, 10 and 25 years return period rainfall. Feasibility of improvement of the Proposed change in longitudinal profile existing storm water drainage network of ON Drain is capable to drain five year or to propose additional network to return period rainfall. Proposed mitigate urban storm water flooding in diversion of flood water from ON Drain the study area. to Coovam river reduces 38% of flood water in ON watershed above Anna Nagar. Both proposals are implementing by PWD in the field. Dissemination of results of the project One inception workshop at Chennai, through workshops/ brain storming three training workshops at Chennai ACKNOWLEDGEMENTS

Min., of Water Resources, Govt. of India for funding the project under Hydrology Project II

PWD and Chennai Corporation for their support in sharing the Hydrological data

Project staff worked under PDS is duly acknowledged for their sincere contribution to the successful completion of the project. Thank you..

Thank you