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ABSTRACT
The
research in this project is to estimate the flood runoff from an
ungauged catchment in eninsular Malaysia using the Soil Conservation
Service (SCS) Method. The objective for the selection of the SCS
Method is to have an alternative method to estimate the flood runoff
from rural, and or mixed development
for ungauged catchments in Penisular Malaysia.
The SCS Method is able to provide
the volume and the peak discharge of a flood hydrograph based on the
rainfall events. Before the SCS Method can be applied to
an ungauged catchment, the parameters of the SCS Method need to be
calibrated from thegauged catchment(s).
The
gauged catchment(s) should have similar land use and physical
characteristics of the ungauged catchment. The physical
characteristics of a catchment are the catchment slope, and hydrologic
soil conditions. The unit hydrograph theory theory is used to
calibrate the SCS Method. The calibrated parameters also known as the
corrected coefficients will then be applied
to SCS Method to estimate the flood
runoff of the ungauged catchment. The flood
hydrographs derived by using the SCS Method will then be compared
with the flood hydrographs derived
by using the Jabatan Pengairan dan Saliran (JPS)
Hydrological Procedures (HP) No. 5,
11, and 16. The HP16 is not forurbanized catchments,
HP5 and HP11 are for rural catchments
condition in peninsular Malaysia.
The
use of Convolution Method
to generate the design
direct runoff hydrographs is used in
the comparison study. In the calibration process, it is
difficult to obtain a good rainfall-runoff relationship
for the gauged catchments. The rain-runoff
relationship of a catchment is determined by the ability of rainfall
stations in or within the catchment boundary to capture the rainfall
events. There are many hydrological records (rainfall and runoff
records) in the sample catchments that are not used in the calibration
process. This is due to the reason that the poor
rainfall records with respect to the runoff records where high
amount of rainfall recorded in one
or two rainfall stations but no records of high runoff in the
streamflow station of the catchment.
Other
reasons are to the missing of either rainfall or runoff
data for the same period of records and difficulty of isolating
single storm hydrograph event where usually the
storms occurred in multiple storm type. There are
limitations to the usage of the SCS Method. These limitations
are due to the lack of soil maps
throughout the Peninsular Malaysia
for soils textural classifications, soils infiltration
rates and land use of the catchment. The land use of the
catchment for agricultural usage for SCS
Method is classified as fallow, row
crops, pasture and others. However, how is the land use of the
catchment relates or equivalent to Malaysian context? For
urban catchment, how is the land
use been equivalent to the terrace houses? With the
calibration of the correction coefficients, it is able to overcome
some the limitations as stated above.
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