DEVELOPMENT OF INTEGRATEDHYDROLOGICAL MODELLING FRAMEWORK FOR
FLOOD INUNDATION MAPPING IN BRAHMANIBAITARANI RIVER BASIN, INDIA
Ravindra Vitthal KaleMEE18715

Supervisors: Professor Toshio Koike
Dr. Katsunori Tamakawa
Dr. Yoshihiro Shibuo
Dr. Yoshiyuki Imamura
Professor Sugahara Masaru
ABSTRACTTo provide aid for operational flood disaster management, this inter-disciplinary research
proposes the conceptualized integrated distributed hydrological modelling framework based on thespatially distributed hydrological models such as the Water and Energy Budget-based Distributed
Hydrological Model (WEB-DHM) and the Rainfall-Runoff-Inundation (RRI) model for floodinundation mapping and flood hazard assessment in the Brahmani-Baitarani River basin, India. Thismodelling framework also takes into account the dam operation impact on the flood inundation in thedelta region. Furthermore, the attempt has been made to extract the flood extent and flood inundation
depth from the MODIS data using GIS based tools such as Modified Gradient Based Method (MGBM)
and FwDET 2.0 tool, respectively. These flood inundation maps derived from satellite data products areused to verify the simulated flood extent and flood depth obtained with proposed integrated hydrologicalmodelling framework. These flood inundation mapping results with both above approaches are foundpromising which warrants its application for the near-real time operational purpose as well as its
transfer to large river basin with similar hydro-climatic and topographical conditions.
Keywords: Flood Inundation Mapping, WEB-DHM, RRI, FwDET, Dam Operation.
INTRODUCTION
Flood inundation mapping is very useful and effective non-structural measure in managing floodrisk and designing food prevention measures to frame flood disaster risk reduction policies. However ,the flood inundation modelling tools for large river basin which are scientifically strong and practicallysimple for flood hazard assessment in near real-time present great challenges to the disaster planningand management authority. The flood hazard assessment in the coastal areas is very complex due to thepresence of multiple reservoirs and irrigation schemes in the river system that control the outflow during
the flooding period and presence of tidal backwaters in low-lying areas of the river system. The dam
operation in a real-time to achieve flood inundation reduction in the delta region is very challenging task
as the existing dam operation are based on the prevailing inflow, storage capacity, pressure to assign
high priority to meet out agricultural and other water demands over flood control activities and outdated
operational rule curves etc. In order to achieve effective reservoir operations and flood reduction indeltaic regions, mainly three types of approaches seem to be promising: (1) integrated hydrologicScientist C, Western Himalayan Regional Centre, National Institute of Hydrology, Jammu, India.
Director, International Centre for Water Hazard and Risk Management under the auspices of UNESCO(ICHARM) Public Works Research Institute (PWRI), Tsukuba, Japan
Research Specialist, ICHARM, PWRI, Tsukuba, Japan
Project Associate Professor, Social Cooperation Program (Flood Risk Management), Water Environment
Technology Lab, Department of Urban Engineering, School of Engineering, The University of Tokyo, Japan
Director for Engineering Policy Analysis, NILIM, PWRI, Tsukuba, Japan
Professor and Director, Disaster Management Policy Program, National Graduate Institute for Policy
Studies (GRIPS), Tokyo

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modelling system to estimate the inflow into and outflow from the water resources controlling structures
such as dams; (2) flood inundation modelling system for deltaic region; and (3) short range rainfall
forecast system such as qualitative precipitation forecast (QPF) system.
Another major challenge in the costal deltaic region is to identify the flood inundation extent
and depth of the flood affected area to plan the disaster management and risk reduction activities during
emergency. Nowadays, the various agencies give information on the areal flood extent, but don’t provide
information on the flood depth, which is very essential for planning evacuation activities as well as flood
disaster risk assessment. Taking into account all these difficulties in the prevention and management offlood disaster, this study sets up the following four specific objectives:(1) To apply the GIS based tools for areal flood extent mapping and flood depth estimation.
(2) To set up integrated hydrological modelling framework for flood inundation mapping.
(3) To evaluate the flood inundation simulation results by the proposed modelling frameworkwith the GIS based flood mapping techniques.
(4) To reduce the flood inundation in low laying area by properly operating dam using the
proposed modelling framework.
THEORY AND METHODOLOGY
In this study, the BrahmaniBaitarani River basin laying in the State of
Odisha and surrounding Jharkhand andChhattisgarh has been selected todemonstrate the application of proposedmodeling techniques for flood inundation
mapping. Figure 1 shows the geographicalareal extent of the Brahmani-Baitarani basin
and the flood extent in year 2008 to 2010.
The basin spreads from 83°55’ to 87°3’ east
longitudes and 20°28’ to 23°38’ northlatitudes. The total catchment area is51907.45 km2. On one hand, there are interstate disputes over water sharing due toreduced water flow in this River basins, which Figure 1: Index map showing the Brahmaniis severely impacting agriculture. On the other Baitarani River basin.
hand, most climate projections show theincrease of precipitation over Brahmani-Baitarani river basin. The Brahmani-Baitarani river basins fallwithin the sub-tropical climate zone, characterized by high temperature, high humidity, medium to highrainfall and short mild winter. The basin area receives an average annual rainfall of about 1400 mm with75 to 80% rainfall occurring during south west monsoon season (June – September).
The upland mountainous river basin area receives very high rainfall over longer duration, whichcause intense flooding in the relatively very flat deltaic region. The flood situation further aggravatedby the high silt deposition at river mouth, flash floods, poor drainage of flood water into sea, breachingof the embankments and coincidence of flood wave with high tidal waves. In recent years, the BrahmaniBaitarani river basin frequently experienced severe floods viz., flood of 2001, 2003, 2006, 2008, 2011
and 2014 (NWM, 2015). Bedsides the major dams like Rengali and Salandi, there are large numbers oftanks, ponds and lakes. As shown in Figure 1, the Rengali dam ( major dam in the Brahmani river basin)
having upstream catchment area of 25,250 km2 plays an important role in controlling floods in the
Brahmani-Baitarani deltaic region. However, downstream from this dam around 10600 km2 area up to
Jenapur (where deltaic region start) is fully uncontrolled. It has been observed that runoff from over
50,000 km2 of catchment area of Brahmani-Baitarani River basin enters the delta, out of which about
50% is fully uncontrolled (NMW, 2015). There is no major diversion channel to control flood in
Baitarani river basin and due to dendrite type drainage network it subjects to flashy floods.
In this study, it is proposed to use the Modified Gradient Based method (MGBM) developed
by Biswas et al. (2016) for flood extent mapping. The flood water depth estimation tool (FwDET v2.0)
2developed by Cohen et al. (2019) and applicable to coastal as well as riverine area flood inundation
mapping is used to estimate the flood inundation depth using the flood extent extracted by MGBM
method and 30 m resolution SRTM DEM of the Brahmani-Baitarani delta region. FwDET v2.0 identifies
the floodwater elevation for each cell within the flooded domain based on its nearest flood-boundary
grid-cell. Therefore, it eliminates the need to utilize the particular datasets without losing the accuracy
and utility. This technique can be used to extract depth from fragmented flood extent map from any
source or resolution means its function independent of sensor or platform. The FwDET v2.0 tool can beused in Python or it can be used as add-in in the ArcGIS software.
Further, an integrated hydrologicalmodelling system is conceptualized with in-built
capability to simulate the hydrologic response oflarge river basin to study the spatial and temporalphysical processes in the Brahmani-Baitarani river
basin, optimization of dam operation and to carryout the flood inundation mapping in the low laying
deltaic region (see Figure 2). As shown in Figure
3, the WEB-DHM and RRI model set-up
conceptualized for the Brahmani-Baitarani basin.
It is proposed to apply the WEB-DHM developedby Wang et al. (2009) to simulate the hydrologicalFigure 2: Conceptual integrated hydrologicalmodelling framework for flood inundation
mapping.
response of the upstream catchments in the BrahmaniBaitarani river basin whereas to simulate the floodinundation in the deltaic region the RRI model (Sayama,2017) developed at ICHARM is applied at the deltaic region.
The WEB-DHM model has capability to be applicable forsimulation of hydrologic response of the large-scale river
basins without compromising the model efficiency. Further,
Figure 3: WEB-DHM and RRI
with improved land data assimilation system based onmodel set-up conceptualized for theobtained reliable parameters and near-surface soil data from
Brahmani-Baitarani basinsatellite, in-situ observations, the WEB-DHM model iscrucial for improving the capability of hazard (Flood anddrought) prediction. However, it is based on 1-D Kinematic wave modelling concept, thus it cannot beapplicable to low laying area like river delta region. It does not have flood inundation mapping capacity.
In order to overcome the limitations of the WEB-DHM model, it is proposed to apply the RRI model,
which uses two dimensional diffusive wave approach to route the runoff on the overland and one
dimensional diffusive wave approach to route the river discharge, to the delta region. The RRI model iscapable to generate the river network and simulate the flood inundation using only the DEM data, whichmeans that it offers simplicity in the modelling. It is important model characteristics where the river
network is very complex as in the coastal region.
DATA
In order to apply GIS based tools to produce the flood inundation extent and depth map, an 8day composite MODIS (MOD9A1) satellite images and 30 m SRTM DEM data downloaded from
USGS website has been used. To set up WEB-DHM model, three kinds of the input data sets are
required to be prepared: namely (a) static data sets; (b) dynamic vegetation forcing, and (c)meteorological forcing. The 30 and 90 m SRTM DEM data is used to for the Baitarani and Brahmani
basin, respectively, to generate the static input data sets. Another static input data such as land use andsoil parameters data prepared using the USGS (1 km grid size) and FAO (9 km grid size), respectively.
All static data sets were resampled to model grid resolution of 500 m. The NK-GIAS software(https://nkgias.com/) is used to prepare all the static data sets. The dynamic vegetation forcing data such3

LAI and FPAR is prepared using 8-day composite MODIS Terra (MODI5A2) satellite product with 500
m grid size. In case of the meteorological forcing, the rainfall data is important input parameter in the
proposed integrated hydrological modelling framework. In this study, the gridded daily precipitation
data at 0.25° from India Meteorological Department (IMD) available for 1960–2015 has been used.
Another required Meteorological data (such as wind speed, specific humidity, and downward shortwave
radiation) are obtained using JRA55 data sets. All these meteorological datasets are prepared using Data
Integration and Analysis System (DIAS). The required topography data sets for set-up of RRI model fordelta region are created using the USGS Hydro
SHEDS (250 m resolution) DEM data. In order tocalibrate and validate the performance of the
proposed integrated modelling framework, thedaily observed gauge and discharge data fromCWC/DoWR at Anandapur, Gomlai and Jenapur(see Figure 3) has been used.
RESULTS AND DISCUSSION
The main objectives of the present study
are to demonstrate the application of GIS based
tools for areal flood extent and depth mapping andto present the integrated hydrological modelling
framework for flood inundation mapping as wellas its application for proper operation of the dam
and to reduce inundation in the coastal area of theBrahmani-Baitarani River basin.
Figure 4 presents the flood inundation
Figure 4. The flood inundation depth estimatedusing FwDET v2.0 based on flood extent map
developed using MBGM method and at top theflood extent map released by NASA (Acquired
on 29 September, 2011).

Figure 5. Spatial distribution of floodinundation (27th September, 2011) simulatedwith the WEB-DHM-RRI model and with
GIS based tools in the Brahmani-Baitarani
Delta.

Figure 6. The Actual and modified reservoir
water levels, average inflow and outflow from theRengali dam before and after dam operation.

Figure 7. Simulated outflow discharge
at the Jenapur site using WEB-DHM
Model before and after dam operation.

extent and depth obtained using MGBM method and
FwDET v2.0 tools based on MODIS satellite data and 30
m SRTM DEM data. These results are attributed to thecapability of the proposed GIS based tools in estimating theflood extent as well as flood depth in the coastal area. The
flood depth estimated by the FwDET method suggests that4

in most of the area, flood depth varies between 1.0 to 2.5 m.
In absence of actual observed water level records, it is very
difficult to compare the inundation flow depth obtained by
FwDET v2.0 method. However, the recent report by National
Water Mission, CWC (India) reported that during the floodingin the Brahmani-Baitarani delta region, the flood water depth
observed in most of the agricultural land area was ranging
between 1.0 to 2.0 m (NWM, 2015). Based on this observation,
it could be concluded that the flood depth estimated by the
FwDET v2.0 can closely represents the real flood inundation
depth in this delta region. The flood inundation mapping
Figure 8. Spatial distribution of results obtained by the WEB-DHM-RRI model for the flood
flood inundation (on 27 September, event of 27th September, 2011 is compared with the flood2011) using WEB-DHM-RRI inundation mapping carried out using GIS based tools as
model in Brahmani-Baitarani delta shown in Figure 5. From the flood inundation mapping resultspresented in this Figure 5, it can be seen that the flood
after dam operation
inundation mapping in the delta region by the numericalapproach and GIS based approach are comparable. However, it should be noted that each approach haveits own advantages and limitations.
Further, the conceptualized integrated hydrological modelling framework in above sections isused to demonstrate its capability in planning of the dam operations and to reduce the flood inundation
extent as well as depth in the deltaic region. As per existing rule curve for the Rengali dam, the waterlevel throughout the September month should be kept at elevation 123.0 (m+MSL). However, heavy
rainfall spell during 2 -9 September, 2011 caused the rising of the reservoir water level not only above
the rule curve level but also above the full reservoir level (FRL) of 123.5 (m+MSL) as shown in Figure
6. The second rainfall spell started from 17th September to 23rd September, 2011. Therefore, from the22nd September, 2011 water level in the reservoir stared building above FRL and on 25th September
reached at very high level of 124.61 (m+MSL). On 25th September, the dam authority has left only with
option of releasing very huge quantity of water through the dam (See Figure 6). As the result, thedischarge of more than 12000 Cumecs was released from the dam which caused the devasting flood
conditions in the deltaic region (see Figure 5). Therefore, in the present study, in order to optimize thedam operations, it has been assumed that the rainfall forecast is available three day in advance. By
knowing possible heavy rainfall spell (generally very challenging task) in next three days, the dam
operations were started on 18th September, 2011 by releasing the volume of water stored above 123.5(m+MSL) to reduce the reservoir water level approximately 1 m below the rule curve level of 123.0(m+MSL) within three days. The maximum water discharge released from the dam was kept 7000
Cumecs which is below the recommended discharge of the 8000 Cumecs (See Figure 6). Note that it isa well-known fact that in the Brahmani-Baitarani delta region, the flood discharge below 8000 Cumecs
causes only small flood damage (NMW, 2015).
Note that the estimated Nash-Sutcliffe efficiency criteria (NSE) to simulate the hydrograph at
Jenapur G&D site using WEB-DHM model as compared to observed data were 0.86 and 0.89 before
and after the dam operation. Similarly, the estimated NSE at Anandapur G&D site (Baitarani basin)using WEB-DHM model was 0.74. The outflow discharge hydrographs simulated (for period 1st June,
2011 to 31st October, 2011) at Anandapur (for Baitarani WEB-DHM sub-basin) and at Jenapur (forBrahmani WEB-DHM sub-basin) are used to define upstream boundary conditions for the RRI modelfor the delta region. Accordingly, the simulated outflow discharges before and after the Rengali dam
operation are shown in Figure 7. It can be seen from Figure 7 that during the period 18th to 26th September,2011 the proposed dam operation resulted in the significant moderation of the peak as well as reductionof peak discharge rate. The simulated flood inundation extent and depth after the dam operation using
the proposed WEB-DHM-RRI modelling framework is shown in the Figures 8. The simulated floodinundation extent and depths (as shown in Figure 8) after dam operation are significantly reduced ascompared to the flood extent and depths before dam operation (as shown in Figure 5). These results
clearly brings out the suitability and necessity of the proposed integrated hydrological modelling
framework in the properly operating the reservoir considering the upstream hydro-meteorologicalconditions to achieve the flood risk reduction in the low laying deltaic region.
5CONCLUSION
In present study, an attempt has been made to address the complex problem of flood inundationin the low-lying Brahmani-Baitarani delta (east coastal areas), India. In order to assist in the emergency
response activities the GIS based tools such as MGBM method and FwDET v2.0 tools for automatic
flood extent and flood inundation depth estimation has been proposed. The proposed GIS based tool
found to be highly promising and could be extended for near-real time application provided that thesatellite data at high frequency could be available. The proposed conceptualized integrated numericalmodeling framework based on spatially distributed WEB-DHM model (to simulate hydrologic responseof upstream watershed area) coupled with two-dimensional diffusive wave based RRI model (for floodinundation modelling in deltaic region) is found to be capable to simulate the watershed response in avery large (51, 907 km2) and complex Brahmani-Baitarani River basins. Further, it was found that this
proposed integrated hydrological modelling framework is very valuable tool to operate the reservoir
properly and significantly reduce the flood inundation extent and depth in the delta region. Therefore, it
is powerful tool to reduce the flood disaster damages and risk.
RECOMMENDATIONIn the present study, it is only demonstrated that how the proposed integrated hydrologicalmodelling framework could be used to reduce the flood damages in the deltaic region by planning dam
operations well in advance. However, there is a need to develop a dynamic system to support reservoir
operators in flood management using real-time observations and weather forecast data.
ACKNOWLEDGEMENTS
The first author would like to express his gratitude to GRIPS and ICHARM for providing thisopportunity to participate in this Flood Disaster Risk Reduction program. The financial support andhospitality received to undertake this course from the Japan International Cooperation Agency (JICA)
is highly acknowledged. He would like to express his deepest gratitude to Dr. S. K. JAIN, Director,
National Institute of Hydrology (NIH) Roorkee for granting permission to undertake this study. Further,
he would like to thanks National Institute of Hydrology Roorkee and Ministry of Jal Shakti, Departmentof Water Resources, River Development and Ganga Rejuvenation, Government of India for providing
this opportunity.
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