Abstract:
Bangladesh is one of the most flood prone countries in the world. To mitigate the
recurrent flood damage, flood forecasting is used as an efficient non-structural flood
induced disaster management system in the country. National level flood forecasting
system is forecasted mainly for river station water level hydrograph and very coarse level
inundation map whereas this study objective is to develop 5 days forecasted flood
inundation map and hydrograph at house level flood information at Rowmari Upazilla of
Kurigram district. This study area is surrounded by the mighty Brahmaputra River and
flashy Jinjiram River. As a result flood occurs every year and destroys agricultural
products of large areas, causes death, damage to property, environmental pollution and
destruction to roads and bridges. A reliable forecast with longer lead time is a way of
reducing the damages.
In this study a weather prediction model (WRF) was coupled with a hydrologic model
and a hydrodynamic model for predicting floods at Rowmari upazilla of Kurigram
district. At first a HEC-HMS continuous hydrologic simulation model is developed for
the Brahmaputra basin based on Soil Moisture Accounting (SMA) algorithm and excess
rainfall was transformed to direct runoff using the Clark unit hydrograph technique. At
the same time, Hydrodynamic Model HEC-RAS 4.1 is setup with geometry data and
observed boundary data. This hydrodynamic model is simulated with unsteady condition
and calibrated and validated with observed water level. WRF 3.2 weather model was
configured and used to predict rainfall over the basin 120 hours into future. Output of the
weather model is incorporated with calibrated and validated hydrologic model HEC-HMS
4.0 and simulated every day during monsoon to forecast discharge at Bahadurabd. This
study has developed three mathematical relations between Bahadurabad station to other
boundary of hydrodynamic model for forecast boundary generation. Then hydrodynamic
model is simulated every day using forecast boundary to generate flood inundation map
and forecast hydrograph at Rowmari Upazilla of Kurigram.
The HEC-HMS application produced satisfactory performance taking into consideration
lumped parameters. Also, among the optimized parameters; Maximum Soil Infiltration
Rate, Surface Storage Capacity, Initial Surface Storage and Tension Zone Storage
Capacity show the higher sensitive. The estimated NSE value for the calibration and
validation period is 0.85 and 0.82. Hydrodynamic Model (HEC-RAS) performance during calibration and validation period in terms of R2 and NSE against observed water
level data is found to nearly 1. The Manning's roughness coefficient (n) and the
coefficient of expansion/contraction (k) are key parameters to calibrate of HEC-RAS
model. Analysis of forecast performance indicates that the forecast for the first 3 days are
good and next 2 days are average to poor according to BWDB guideline. This developed
flood forecasting system is capable of predicting the inundated area of Rowmari Upazilla
during a monsoon season.
