Application of Rorb Rainfall-Runoff Model to Urban and Rural Catchments
Over the years, many have realised the growing importance of water and its resources to sustain industrial and community development and most importantly life in all forms. However, excess of uncontrolled surface runoff could lead to flooding and potential damages in properties and loss of life....
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| Main Author: | |
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| Format: | Thesis |
| Language: | English |
| Published: |
2004
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/5898/1/FK_2004_18%20IR.pdf |
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| Summary: | Over the years, many have realised the growing importance of water and its
resources to sustain industrial and community development and most importantly
life in all forms. However, excess of uncontrolled surface runoff could lead to
flooding and potential damages in properties and loss of life. As a result, the field of
hydrology and hydraulic has become a growing importance. With the current
technology, various software programs are developed to assist in the analysis and
study of water resources management and flood mitigation. Amongst them is the
Rainfall-Runoff Routing Model which was widely used in Australia. It has also
been used in some of the catchments' studies and flood mitigation projects in
Malaysia, mostly to perform flood routing and estimation.
The primary aim of the study is to assess the suitability of RORB model for
application to catchments in Malaysia. It is used to simulate the rainfall-runoff
routing process of two characteristically different catchments namely Sg Klang
Basin at. Tun Perak Bridge and Sg Bernam Basin at South Kinta Consolidated Bridge. The former is highly urbanised and located in Wilayah Persekutuan while
the latter is considerably rural and encompasses both Perak and Selangor states.
The setting up of the model begins with subdividing the catchment into various
subcatchments based on catchment topography, river system and drainage divides
which are then modelled by a series of links and nodes, which represent the reaches
of flow and subcatchments respectively. Next, the various input parameters such as
subcatchment area and landuse condition, channel type, length and slope, fraction
imperviousness, rainfall and streamflow data are defined and determined. All these
are compiled in an input data file which is written in Fortran language following a
specific sequence of command codes for running of the model simulations.
The catchment modelling is performed up to the calibration and verification stage using
4 storm events; 2 each for calibration and verification respectively. These events are
identified based on available past 3 to 40 years of rainfall and streamflow records
collected from Department of Irrigation and Drainage Malaysia. The best fit model
parameters, m and b, are determined and the results of the generated runoff
hydrographs are compared to the observed hydrographs.
The model is areally distributed, nonlinear, and has a linear or non-linear storage
relationship between storage S and outflow discharge Q which is given as:
S = kckrQm
where kc and m are the catchment parameters determined by trial and error fitting
while kr is relative delay applicable to individual reach storage calculated based on
any unit of indicator of storage delay time. Two units of indicator, namely flow length and flow time, are adopted separately in 1" Model Setup and 2nd Model Setup
to ascertain the sensitivity of these two units to the model and its results.
This study concludes that the application of RORB model is relatively user friendly.
Also, the model is less complicated in its application as it does not involve too many
input parameters leading to less assumption to be made. This is an advantage in
view of the inherent problem of data inadequacy and poor quality of recorded data.
In addition, there are only two model parameters, m and k,, to determine because of
the simplified approach to the rainfall-runoff process.
The study also showed that ROD model is applicable to both urban and rural
catchments. The overall results indicated variations of less than 10% between the
generated and observed runoff discharges and volumes, which is of acceptable
limitation. However, it is also shown SKC catchment has a higher variation than
Tun Perak catchment. This is most possibly due to the fact that SKC catchment has
a very much bigger catchment area about 10 times greater than Tun Perak
catchment. This results in larger propagated errors or discrepancies in the
modelling. But overall, the peak times and shape of the runoff hydrographs are
generally matching between the observed and generated. Finally, the model is also
not sensitive to the types of indicator used for relative storage delay time as the
maximum variations in the results between the two model setups are 2%.
In conclusion, RORB is an acceptable model which provides a reasonably good
simulation of the rainfall-runoff process in a catchment |
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