Flood Plain Modelling using River Hydraulic Modelling Approach

Abstract

Flood inundation is a natural disaster which almost every year accounts for loss of properties as well as human lives in different regions across the world. The present study was carried out to simulate and map inundated areas of Alaknanda, Mandakini and Bhagirathi rivers in the region of Rudraprayag and Uttarkashi of Uttarakhand respectively using hydraulic modeling on GIS based HEC-GeoRAS platform through detailed parameterization of river channels. In year 2013, there was huge devastation in Rudraprayag and Uttarkashi area due to heavy flooding. This study estimates the loss occurred during this event as well as presents future flooding scenarios through simulation modelling. To carry out the research, a high resolution imagery of Google Earth was employed for visualization, LULC extraction, delineation of flood hazard maps and to increase accuracy of hydraulic model. A digital elevation model of Cartosat-1 stereo data (1 arc degree vertical resolution) was used to extract elevation related information. Total six flood plains for each river were simulated using river flow data. The first river flow data having least value was the real flow data related to flood event of 2013 while other flow data were hypothetical and were used to simulate flood plains so that future scenarios could be generated as well as mapped and loss to various LCLU categories can be measured. The velocity mapping was also performed through water surface profiles. It was observed through the analysis that flood events of similar degree of 2013 or higher may account for considerable loss to agriculture, built-up areas and roads. In Uttarkashi region, agriculture, built-up areas and roads were found to be damaged while due to a good distance of agriculture from river plain, there was no loss to agricultural land in Rudraprayag area but built-up areas and roads were found to be affected by flood water. This type of simulation study is very much helpful to policy makers and disaster managers for their preparedness to any forthcoming flood event. Keywords: HEC Models, ArcMap, HEC GeoRAS, Flood simulation Modeling, Inundation Mapping, River Hydraulic Modeling

Full text

Flood Plain Modelling for Rudraprayag
and Uttarkashi areas using River
Hydraulic Modelling Approach
Gopal Krishna, R N Sahoo,
V K Sehgal & Ravender Singh
Division of Agricultural Physics
Indian Agricultural Research Institute, New Delhi

Overview •Objectives
•To simulate flood plain for estimation of the
extent of flood.
• To delineate inundation areas in the region
of Rudraprayag and Uttarkashi (Alaknanda,
Mandakini and Bhagirathi rivers
respectively).
•Estimation of losses and Vulnerability
analysis for different scenarios / LULC
categories.
•The Flood plains was simulated
through HEC-RAS one dimensional
model.
•The Arc GIS has HEC - Geo RAS
extension developed by ESRI and
HEC. This extension is a very
essential tool for flood plain mapping,
velocity mapping and water surface
profiles generation.
•The Satellite image was obtained from
Google earth and was registered
using ENVI Image processing
software.

Water
surface
profiles
HEC-RAS
Flow
Discharge
Data
Geometric
data
Steady
Flow
Analysis
Arc GIS with HEC-Geo RAS
Flood
Plain & velocity Maps
Generation
Methodology
Input River Geometry generation in
ArcMap
Arc GIS with HEC-Geo RAS

Legend
tin_rp
Elevation
1280 - 1380
1180 - 1280
1080 - 1180
980 - 1080
880 - 980
780 - 880
680 - 780
580 - 680
TIN_Rudraprayag
River Centerline
Cut Lines
TIN_Uttarkashi
Legend
tin_Masspoints
Elevation
1632 - 2040
1224 - 1632
1003 - 1224
666 - 1003
0 - 666
3D View of Study Area with River CL & Cutlines

Alaknanda & Mandakini
River Near Rudraprayag
4
0170 340 510 68085 Meters
Input Geometry for River Analysis System with TIN
Uttarakhand State -
DEM
Uttarkashi
Rudraprayag
0 480 960 1,440 1,920240 Meters
4
Bhagirathi River Near Uttarkashi

Uttarkashi
Year
Flow rate/Range of
Discharge (Cumec)
Catchment Area
(Km2)
River
1989-90 to 2008-09
1.8 to 1011
4555
Bhagirathi
Rudraprayag (Before Confluence)
1989-90 to 2008-09
49 to 2873
1644
Mandakini
Rudraprayag (After Confluence)
1989-90 to 2008-09
50.7 to 3762
10675
Alaknanda
At the time of flash
flood the flow rate
was recorded as
1110 cumec at
uttarkashi and
~4000 cumec at
Rudraprayag (after
confluence).
Source : CWC
Flow Rate data used for flood plain generation

3D Map of Rudraprayag city with floodplain profile overlaid
River
Flood Plain with profile4
Agriculture
Built-up Area
Roads
Results

Area in Hectare
Damage Estimation by
Flood plain/Category
Agricultural
Land (ha)
Built-up Area
(ha)
Roads
(ha)
Total damaged Area
(ha) in given three
LULC Classes
Damage by flood plain 1
No Loss
4.30
2.04
6.34
Damage by flood plain 2
No Loss
5.38
2.15
7.53
Damage by flood plain 3
No Loss
5.87
2.20
8.07
Damage by flood plain 4
No Loss
6.39
2.25
8.64
Damage by flood plain 5
No Loss
7.07
2.30
9.36
Damage by flood plain 6
No Loss
7.34
2.32
9.67
Total Area (Hectare) before
flood
15.10
20.05
7.25
Damage Estimation by Simulated
flood Plains in Rudraprayag
Legend
LULC Classes
Agriculture
Bridge
Bulitup Area
Hilly Area
River
Road

River
Flood Plain with profile4
Agriculture
Built-up Area
Roads
Results
3D Map of Uttarkashi city with floodplain profile overlaid

Legend
River
LULC Classes
AGRICULTURE
BRIDGE
BUILTUP AREA
HILLY AREA
POWER PLANT
ROAD
Damage Estimation by
Flood plain/Category
Agricultural
Land (ha)
Built-up Area
(ha)
Roads
(ha)
Total damaged Area
(ha) in given three
LULC Classes
Damage by flood plain 1
28.66
34.65
0.58
63.89
Damage by flood plain 2
34.00
37.75
0.61
72.37
Damage by flood plain 3
38.76
41.86
0.63
81.26
Damage by flood plain 4
41.80
44.14
0.65
86.58
Damage by flood plain 5
44.25
46.11
0.64
91.00
Damage by flood plain 6
48.66
46.65
0.65
95.96
Total Area (Hectare) before
flood
383.16
143.21
9.43
Damage Estimation by Simulated
flood Plains in Uttarkashi
Total Agriculture
in study
area 383.16 ha
Total Built-up Area
=143.21 ha
Total Roads in Study
Area 9.43 ha

Validation
•As per information released by
Uttarkhand principal secretary
(agriculture), about 20,000ha of
agricultural land was severely
damaged in Uttarkashi, Chamoli
and Rudraprayag districts.
•According to a rough estimate, in
Uttarkashi city and its surrounding
areas, approximately 43 ha
agricultural area was inundated
which is very much close to our
model’s prediction as 41.80 ha.
•Non-availability of satellite data in
optical region is a constraint
during rainy season.
•The elevation data may have some
erroneous information at some
points, resulting in misinterpreted
results.
•Non-availability of flow data at
every station is also a major issue
which may affect the accuracy of
model.
Limitations

Conclusions
•The HEC Geo RAS an extension of RAS with Arc GIS has exeptional
capability to support the model building process.
•There no loss to agriculture was found in Rudraprayag area with a
maximum of 9.67 ha for all LCLU classes while in Uttarkashi the damage
was found up to 95 ha for all LCLU classes.
•In Rudraprayag, Built-up area was found to be the most affected class
while in Uttarkashi, Agricultural land was the worst affected.
•Using the fifth and sixth flood plains, the potential prediction of loss to
land-use and land-cover class may be done which is helpful for policy
makers and resource managers too.

Thank you