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10. No. 1 Spring 2010
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Flood susceptible mapping and risk area delineation using
logistic regression, GIS and remote sensing
Biswajeet Pradhan
Abstract:
Recently, in the year 2006, 2007 and 2008 heavy
monsoons rainfall have triggered floods along Malaysia's east
coast as well as in different parts of the country. The hardest
hit areas are along the east coast of peninsular Malaysia in the
states of Kelantan, Terengganu and Pahang. The flood cost nearly
millions of dollars of property and many lives. Foods are
considered to be one of the weather-related natural disasters.
Many methods exist to provide qualitative estimations of the
risk level of flood susceptibility mapping within a watershed.
This paper presents construction of a flood susceptible map for
presumptive flood areas around at Kelantan river basin in
Malaysia using a statistical model and GIS. To evaluate the
factors related to flood susceptible analysis, a spatial
database was constructed from a topographical map, geological
map, hydrological map, Global Positioning System (GPS) data,
land cover map, digital elevation model (DEM) data, and
precipitation data. An attribute database was also constructed
from field investigations and historical flood areas reports for
the study area. Logistic regression model was applied to
determine each factor’s rating, and the ratings were overlaid
for flood susceptibility mapping. Results indicate that flood
prone areas can be performed at 1:25,000 which is comparable to
some conventional flood hazard map scales. The flood prone areas
delineated on these maps correspond to areas that would be
inundated by significant flooding. Further, risk analysis has
been performed using DEM, distance from hazard zone, land cover
map and damageable objects at risk. DEM was used to delineate
the catchments and served as a mask to extract the highest
hazard zones of the landslide area. Qualitatively, the model
seems to give reasonable results with accuracy observed was 85%.
Key words:
Flood susceptibility
analysis; logistic regression model; GIS; Remote Sensing
Abstract:
Twelve
Vertical Electrical Sounding (VES) were carried out using
Schlumberger configuration in parts of Kaushambi district
(latitude 25o 15' 8'' and 25o 39' 55''
N. and longitude 81o 17' 5'' and 81o
31' 5'' E) Uttar Pradesh to determine the nature and
thickness of aquifer zone and necessary geoelectrical
parameters. The data were interpreted with the help of three
and two layer master curves and auxiliary point charts.
Sounding curve suggests number of three layer geoelectrical
sections H, A, K, Q type and some of four layer section of
the KHA, QHA, HA, types. The study indicates that average
depth of the top of the aquifer is 35 m and average
thickness of the aquifer is 53 m. The bedrock is encountered
at an average depth of 89m. This study indicates that the
groundwater reservoirs are mainly confined to the alluvial
aquifer.
Keywords:
Groundwater/
Vertical Electrical Sounding (VES)/ Resistivity
Abstract:
Geomorphologic instantaneous unit hydrograph (GIUH) can be used
as a transfer function for modeling the transformation of excess
rainfall into surface runoff, in which excess rainfall is an
excitation (i.e. production function) to the hydrologic system.
These models can be used to predict / forecast the temporal
variation of the surface runoff at the outlet of ungauged basin,
which is useful in the hydrologic / environmental engineering
applications. The present study deals with the geomorphometric
investigation and provides an efficient solution approach to
derive the GIUH based transfer function and thus geomorphologic
unit hydrograph (GUH) for the basin. Since, Gomti river basin is
ungauged, therefore, to test the effectiveness of the approach
two cases were considered. Firstly, the approach was tested on
the catchment for which published UH data was available; and
secondly, the approach was applied for the Gomti river basin for
the derivation of GUH. To verify the derived GUH of the Gomti
basin, a comparison was performed with the synthetic unit
hydrograph (SUH) obtained from the Central Water Commission (CWC)
procedure. Based on the comparison of the result, it may be
revealed that the GUH with dynamic flow velocity of 0.68 m/s was
close to the SUH.
Key words: Basin, CWC, Direct runoff; Geomorphology; Gomti river;
Geomorphologic instantaneous unit hydrograph; Transfer function;
Geomorphologic unit hydrograph, SRTM, Synthetic unit hydrograph,
Ungauged basin
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Abstract:
The Manning’s
roughness coefficient (n) is commonly used to represent surface
roughness in lumped and distributed hydrologic models. Model
parameter sensitivity studies identify runoff response to be
sensitive to Manning’s n changes. For large watersheds, modelers
typically use land use / land cover datasets to assign Manning’s
n values based on the use or cover class (e.g., residential,
impervious). Although this approach is expected to introduce
errors to the simulation results, studies have not adequately
assessed the occurrence or magnitude because of the challenge of
producing an accurate Manning’s n map to compare to a map
produced by the land use / land cover approach. This paper
presents a watershed scale assessment of the hydrologic model
error incurred by use of land use / land cover datasets to
estimate Manning’s n. A digital dataset of Manning’s n is
generated by manual inspection of aerial photos for a 23 km2
watershed. Manning’s n is also estimated using the land use
classes in the National Land Cover Dataset (NLCD). Up to 50%
difference in the magnitude and variation in spatial
distribution of Manning’s n values is found in more than 90 % of
the study area. The differences did not translate into
significantly altered runoff responses (hydrograph magnitude: 9
% to 22 % relative peak discharge difference and shape: 2 % to
18 % relative time to peak difference) from 3 storm events at
the watershed outlet for a lumped model (SWMM) and a distributed
model. However, these differences are significant (up to 75 %
relative peak discharge difference and up to 300 % relative time
to peak difference) at the subcatchment levels and showed
increasing trend in deviation of the hydrograph peaks with
increased Manning’s n deviation. The results of this study
suggest that the use of NLCD-defined Manning’s n values is
acceptable for medium to large watersheds.
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Evaluation of total runoff for the Rio San Pedro sub-basin
(Nayarit, Mexico) assessing their hydrologic response units
Rafael Hernández Guzmán, Arturo
Ruiz-Luna, César Alejandro Berlanga-Robles and Zoltán
Vekerdy
Abstract:
The Rio
San Pedro sub-basin runoff was estimated using the curve number
method (NRCS-CN) applied to hydrologic response units (HRU’s),
derived from remote sensing and GIS analysis. The sub-basin
(around 2900 km2) was delineated from digital
elevation models (DEM), that also were used to obtain the slopes
in the study area. A landscape characterization (overall
accuracy > 80%), based on Landsat ETM+ imagery, was obtained
using standard classification methods, and together with a
rainfall data series, were the input information for the
sub-basin discretization in HRU’s and the runoff calculation.
Seventeen HRU’s were obtained, that can be arranged in three
main groups. HRU’s associated to forest and high relief areas,
representing 2/3 of the total area and contributing up to 71% of
total runoff. The land covers related with human activities
integrate a second HRU’s group, contributing with 20% of runoff,
although they represent less than 15% of the area. Finally
wetlands and aquatic surfaces, not contributing to runoff, are
the third HRU group. Because of the measures of accuracy
correspond to good agreement between the model and the reference
data, the HRU’s approach that retains the spatial heterogeneity,
is considered a fine approximation for the San Pedro sub-basin
runoff assessment that can be integrated to the development of
environmental management programs.
Key words:
Runoff, hydrologic response unit, curve number, land uses, GIS,
DEM.
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JoSHJournal
of Spatial Hydrology
ISSN: 1530-4736