FLOOD MODELLING OF KALU-GANGA RIVER
BASIN
H. K. Nandalal
Department of Civil Engineering
University of Peradeniya
Peradeniya
Sri Lanka
Problems related to flooding have greatly increased
over recent decades because of
population growth
development of extensive infrastructures in close
proximity to rivers
It is importance to find solutions by
utilizing modern technology like Geographic Information
Systems (GIS), Remote Sensing (RS) and
flood modeling
Study area
Data used
Software used
Application of Software
HEC-HMS
HEC-RAS
ENVI
Kalu-Ganga river basin in Sri Lanka
 Total catchment area is 2719 km2
 Entire basin lies within the wet
zone.
 Average annual runoff is around
7600 MCM.
 Catchment experiences average
annual rainfall of 4000 mm.
 Study concentrates on the lower reaches of the river
 Area of interest is nearly 500 km2
 This includes 5 Divisional Administrative Divisions (DSD)
TIN Model of the Study area
LIDAR DATA
Contour Data
Locations of rainfall and discharge gauging stations
Satellite images
Raw Images (Dry Date, 03 March,2008)
ALOS – PALSAR (HH)
Raw Images (Wet Date, 03 June,2008)
ALOS – PALSAR(HH)
Data Collection and Data-basing…
Rainfall –Runoff Modeling
Basin model developed using HEC-GeoHMS
Results of the verification runs to compare the simulated flows
and the observed flows of the calibrated HEC-HMS model
Flood Modeling
Geometric Data: HEC-GeoRAS export
 Stream C/L
 River banks
 Flow paths
Discharge data obtained from HEC-HMS
Mawakoya
Elagawa
Junction Mawakoya/Kalu Ganga
Kuda Ganga
Junction Kuda Ganga/Kalu Ganga
Flow (m3/s) data at\Return Period
10yr
20yr
50yr
100yr
Elagawa
1062.6
1319.7
1798.1
2605.5
Junction KudaGanga/ Kalu Ganga
1455.7
1836.9
2524.4
3743.3
97.5
122.2
174.4
245.5
1079.5
1340.5
1828.5
2647.7
414.4
555.3
817.1
1260.7
Mawak Oya
Junction Mawak Oya/Kalu Ganga
Kuda Ganga
HEC-RAS output
HEC-RAS output
Flood Hazard Maps from HEC-RAS
Raw Images (Dry Date, 03 March,2008)
ALOS – PALSAR (HH)
Raw Images (Wet Date, 03 June,2008)
ALOS – PALSAR(HH)
(Difference dB image Wet - Dry)
Mask