Rainfall-runoff Simulation and Modeling of Karun River Using HEC-RAS and HEC-HMS Models, Izeh District, Iran
This study developed a framework for regional scale flood
modeling that integrates GIS and two hydrological models. Hydrologic Engineering
Center-Hydrologic Modeling System (HEC-HMS) and Hydrologic Engineering Center-River
Analysis System (HEC-RAS) models are used to simulate and model relations between
rainfall and runoff in Karun River, SW Iran. The Karun River is the domain of
the study because it is a region subject to frequent occurrences of severe flash
flooding. The model consists of a rainfall-runoff model (HEC-HMS) that converts
precipitation excess to overland flow and channel runoff, as well as a hydraulic
model (HEC-RAS) that models unsteady state flow through the river channel network
based on the HEC-HMS derived hydrographs. For model calibration, the simulated
results were compared with the observed water storage data for several storm
events. The same rainfall event in Izeh district generates almost twice as much
of the surface water runoff generated in each of other downstream. This is mainly
attributed to the large catchment area of Izeh basin as compared to the other
two basins. The modeling framework presented in this study incorporates a portion
of the recently developed GIS tool named Map to Map that has been created on
a local scale and extends it to a regional scale. The results of this research
will benefit future modeling efforts by providing a tool for hydrological forecasts
of flooding on a regional scale. While designed for the Karun River, this regional
scale model may be used as a prototype for model applications in other areas.
Received: June 04, 2012;
Accepted: August 25, 2012;
Published: September 08, 2012
Flood events are defined as the occurrence of severe storms. With increasing
average global temperature trend to exacerbate climate events has been increased
(Behbahani et al., 2006; Bates,
2004; Borga, 2002). So with regard to climate change,
the need to provide reliable models in flood modeling is high. Increasingly,
for environmental planning, due to the development of regulatory and planning
tools, such as the river basin masterplan, there is need to such models for
flood forecasting and river management. Usually, morphologic analyses are used
for the delineation of river floodplain, but for the computing of the flood
return period there is need to using computational hydraulic-hydrologic models
(Clark, 1945; Anderson et al.,
2002; Ahrens and Maidment, 1999; Bedient
et al., 2003).
Similarly, there is a need to establish rules for the use of water resources,
for instance when authorizing the maximum rate of abstraction for irrigation
taking into account the water budget for the whole basin (Freeze
and Harlan, 1969; Gasim et al., 2012).
Planning a river basin master plan has a need for planning the procedures of
basin and its design, that both of them are based on shared databases and computational
procedures (Becker and Grunewald, 2003; Beven,
2002; Garrote and Bras, 1995). The evaluation of
areas at risk and the implementation of measures of risk mitigation delineate
a dynamic context in which an upgraded representation of the river network and
its hydrologic parameters play a relevant role in supporting environmental as
well as urban planning.
Recent researches conducted in the field of flood modeling have focused mainly
on using ArcGIS utilities. This modeling extension allows coping with quasi-2D
aspects of flow through connecting the river geometry with a digital terrain
model in the form of a Triangulated Irregular Network (TIN) (Gholami
et al., 2009; Alireza and Nabavi, 2007; Razi
et al., 2010). In this way, the distributed output provided by HEC-RAS
for each cross section is interpolated between cross sections and results in
a water depth and a water velocity surface. When compared with a fully-2D flow
model, the only limitation is in giving a flow velocity which disregards transversal
components of the flow field vectors, on their side usually deemed negligible
in stream hydraulics (HEC, 1996a, b,
Based on the above sketched model, it is possible to map with appreciable realism
the morphology of river and floodplain and to detect the flooded areas for a
discharge and flood hydrograph with given return period.
Robayo et al. (2004) had presented a method
using the MAP to MAP, time series of rainfall from weather radar and hydrological
models for flood modeling. The model HEC-RAS delineates a fully functional modeling
environment which allows coping with virtually all types of problems concerning
river networks. In the application case described below, the advanced capabilities
of the software for modeling hydraulic singularities such as bridges and weirs
was exploited to derive theoretical rating curves based on steady non uniform
flow. The purpose of this study is to understand hydrologic behavior of the
Karun River in Northern Izeh district and planning for development of rural
in vicinity of river bank.
MATERIALS AND METHODS
Study area: Karun River is located in Southernwest of Iran between 49°54'48to
49°5458E and 31°5912 to 32°N. Six catchments
of the Karun River, Northern Izeh, Iran, are selected for this study (Table
1) in a 2.5 Km length of Karun River. These catchments have different physiographic
specifications (Table 2). Figure 1 shows
study area location in Iran. Runoff measurements of six hydrometry stations
are collected in a 3 year period from 2008 to 2011. Topographic and climatic
conditions of these sub-catchments are mostly the same. Rainfall-snowy regime
are dominant in all sub-catchments. Average rainfall of the study area is about
650 mm/year (WMO, 2003). Dry season starts at June and
ends at November.
In this research, steady flow was simulated along 2.5 km of Karun River, SW
of Iran. HEC-RAS simulation model in combination with GIS capabilities was used
for this purpose (Fig. 2). After preparing the project file,
a TIN theme was extracted based on georeferenced field cross sections and topographical
data in order to prepare required data to be processed. Topographic map with
scale of 1:25000 and river plan with scale of 1:1000 were applied for TIN generation
using 3D analyst capability of ArcGIS. The HEC-GeoRAS extension is used in conjunction
with 3D analyst for interpolation of digital terrain data and Spatial Analyst
for proper display of the cross sections. The stream centerline and left and
right channel banks, flowpath and cross section cut lines themes have prepared
and then generate RAS GIS import file for hydraulic simulation in HEC-RAS model
(Salimi et al., 2008).
Rainfall-runoff model HEC-HMS: The Geospatial Hydrologic Modeling Extension
(HEC-GeoHMS) uses ArcGIS and Spatial Analyst to develop a number of hydrologic
modeling inputs. Analyzing digital terrain information, HEC-GeoHMS transforms
the drainage paths and watershed boundaries into a hydrologic data structure
that represents the watershed response to precipitation. Rainfall-Runoff modeling
was performed using the Hydrologic Engineering Centers Hydrologic Modeling
System (HEC-HMS version 3.0.1) importing results from HEC-Geo-HMS (Feldman,
|| Details of studied sub-catchments
|| Calibrated parameters for studied sub-catchments
|| Location of study area in Iran
|| Flowchart that shows how models are running
This model developed by the US Army Corps of Engineers, is designed to simulate
the precipitation-runoff processes of dendritic watershed systems (HEC,
2002; Brunner, 2001). The physical representation
of the watershed is accomplished with a basin model. Various hydrologic elements
are connected in a dendritic network to simulate runoff processes (Jayakrishnan
et al., 2004; Horritt and Bates, 2002; Lamidi
et al., 2008).
Hydro-dynamic model HEC-RAS: HEC-RAS, developed by the United States
Army Corps of Engineers Hydrologic Engineering Center, is intended for performing
one-dimensional hydraulic calculations for a full network of natural and constructed
channels. The system can calculate water surface profiles for both steady and
unsteady gradually varied flow. The steady flow system is designed for application
in flood plain management studies (Reed and Maidment, 1995;
Rinaldi et al., 2012; Azar
et al., 2012). Also, capabilities are available for assessing the
change in water surface profiles due to channel improvements and levees. HEC-GeoRAS,
an ArcGIS extension, creates a HEC-RAS import file containing geometric attribute
data from a Digital Terrain Model (DTM) and performs post processing of results
exported from HEC-RAS.
Statistical analysis: Topographic map and detailed thematic map of the
Izeh district are feed in HEC-RAS and HEC-HMS models. Digital Elevation Model
of the study area is base map for outputs. Main parameters needed are cross-sections
for river and flood plain including left and right bank locations and flow paths,
roughness coefficients (Mannings n) and contraction and expansion coefficients
(Giannoni et al., 2003; Hudson
and Colditz, 2003; Grassotti et al., 2003;
Dastorani et al., 2010). A variety of methods
are available for simulating infiltration losses, transforming excess precipitation
into surface runoff, computing base-flow contributions to subbasin out flow,
flow routing etc. Outflow from a sub-basin is computed from rainfall data by
subtracting losses, transforming excess precipitation and adding base flow.
RESULTS AND DISCUSSION
Frequency analysis of peak flow data was conducted to select the most accurate
input for the hydraulic simulation of the river reach. It has shown that Log-Pearson
III is the best distribution to estimate peak flow in different return periods,
regarding to the least differences between observed and estimated peak flow
(Dastorani et al., 2011; Wadsworth,
1999; Townsend and Walsh, 1998). Table
3 has shown magnitude of peak flow in 2-100 years return periods. Peak flow
estimated using flood frequency analysis was used as the steady flow data for
simulation. In this table, first column is river name that is same for all parts
of the study area. Second column is station name. Profile column shows return
period of floods. Q-total is total discharge (m3 sec-1),
max. channel elevation is elevation of each station. W.S. elevation is elevation
of water surface and Crit. W.S. is critical water surface (in meter). Flow area
is area that flood covers. Top width is maximum of elevation of flood surface
and Froude Chl. is Froud number that can be critical, sub-critical of hyper-critical.
Normal depth for upstream and critical depth for downstream was considered as
boundary conditions for this analysis. Other inputs such as Manning`s n value,
river system schematic, contraction and expansion coefficients, flow regime
entered to model and HEC-RAS model has run for steady flow and mixed flow regime
(Shokoohi, 2007; Vieux and Bedient,
Flood levels in one of the analyzed cross sections can be shown in Fig.
3 and 4. There is more than 1.5 m difference between flood
levels in two mentioned return periods. One of the most important results of
HEC-RAS simulation is preparing different water surface profiles of different
T-year floods. In the next step, the results of hydraulic simulation within
HEC-RAS model were exported to GIS for floodplain delineation and further analysis.
Delineation of flood extents and depths within the floodplain of Karun River
was conducted in different return periods based on the integration of hydraulic
simulation results and GIS analysis using the HEC-geoRAS extension of ArcGIS.
|| Outputs of HEC-RAS model in Karun river
|Profile: Return period of floods, Q-total: Total discharge,
Min. channel elevation is elevation of each station. W.S. Elev: Elevation
of water surface, Crit. W.S.: Critical water surface, Flow area: Area that
flood covers, Top width: Maximum of elevation of flood surface, Froude Chl.:
Froud number that can be critical, sub-critical of hyper-critical
|| Cross sections in (a) 923.2031, (b) 1469.997, (c) 1775.510
and (d) 1945.380 stations in the study area
|| Longitudinal profile of Karun river in the study area considering
return time of floods
Figure 3 and 4 have shown flood affected
area for the 2 and 100 years flood events, as a sample in the study area.
Hydraulics simulation for floodplain mapping could be beneficiary in several
aspects for land and water resources management and also engineering purposes.
It can be applied to prevent unwise land use in flood prone areas and flood
insurance studies, based on modeling of water surface elevations for design
flood events (Whiteaker and Maidment, 2004). The design
of bridge and culvert openings for roadway crossings of streams and consequences
of flood reduction measures such as dams, levees and channel modifications could
be predicated on proper floodplain hydraulic analysis. Increasing the size,
slope, or depth of the channel or decreasing its roughness can lead to a reduction
in flood levels because of the additional channel capacity. On the other hand,
channel modifications can also have negative effects, such as increasing in
flow velocity which could be simulated using hydraulic model.
Sensitivity analysis of hydrologic parameters: Sensitivity analysis
of run-off lag time calculated using two methods (SCS and Snyder) shows high
sensitivity of this parameter in the range of 0 and -30%, means that the catchment
discharge is more sensitive to smaller values of lag time. In the other word,
underestimation of lag time would cause more error on prediction of discharge
in comparison to overestimation of this parameter. In addition, outputs of the
model are slightly more sensitive to lag time calculated by SCS method than
that calculated by the Snyder method (US/SCS, 1986).
Verification of the model: Table 3 show the predicted
peak discharge and time to peak and the related observed values for a rainfall
event used for verification of the model. The results show that calibration
of parameters such as CN and initial loss could considerably improve the outputs
of the model. The most important findings of the research can be concluded as
||Comparing the outputs of the model in two different conditions
(using SCS and Snyder methods) to the observed values indicates priority
and robustness of SCS method for run off estimation (both in peak flow and
lag time) in ungauged catchments
||The HEC-HMS program is a generalized modeling system capable of representing
many different watersheds. A model of the watershed is constructed by separating
the hydrologic cycle into manageable pieces and constructing boundaries
around the watershed (Razi et al., 2010)
||Initial loss, curve number, impervious area, lag time, initial discharge
are determined through calibration process where the parameters are adjusted
until the observed and simulated hydrographs are close fit. By using soil
hydrologic type classifications with soil maps and land use type classification
tables with land-use maps, the Curve Number (CN) map was constructed
||For model calibration, the simulated results were compared with the observed
water storage data for several storm events (Fig. 5).
The same rainfall event in Izeh district generates almost twice as much
of the surface water runoff generated in each of other downstream. This
is mainly attributed to the large catchment area of Izeh basin as compared
to the other two basins. The modeling framework presented in this study
incorporates a portion of the recently developed GIS tool named Map to Map
that has been created on a local scale and extends it to a regional scale.
The results of this research will benefit future modeling efforts by providing
a tool for hydrological forecasts of flooding on a regional scale. While
designed for the Karun River, this regional scale model may be used as a
prototype for model applications in other areas
|| Flood zonation of Karun River in the study area using HEC-RAS
The modeling system here presented copes with a basic need of standardization
of the databases. The main goal is to provide an environment in which all computations
made by the different regional and municipal offices involved in river training,
hydraulic works and similar activities can converge, share the same fundamental
assumptions as far as roughness coefficients and hydrologic data are concerned
and keep a continuous updating of the database including ongoing works, so to
have a consistent and always realistic representation of the river network,
its critical reaches and the priorities of intervention. Application of hydraulic
modeling in GIS environment provides the capability to simulate flood depth
in different part of the floodplain.
The need of such a modeling system is stimulated and sometimes even enforced,
by the many activities required by river basin planning and management, ranging
from flood timely alert to the individuation of areas at risk of flooding, to
the programming of water budget at the basin scale, according to the national
and regional regulations in the field. The main trouble with the construction
of such a consistent and self-updating database is in that many different offices
have been so far working separately in the field of hydraulic protection, river
training and related public works. The availability of comprehensive software
in the public domain allows to link databases to computing and design tools
so to allow a strict pipelining of the activities of database construction,
river basin planning, management, programming and financing of the interventions
and design and construction of the works.
The authors would like to thank the Islamic Azad University, Behbahan branch
for the support of this research. Contribution of Khuzestan Water and Power
Authority is also acknowledged.
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