Hamidreza Babaali; Zohreh Ramak; Reza Sepahvand
Abstract
Introduction: Estimating the design flood of the basin for the design of hydraulic structures, stabilization of river banks, watersheds and flood zoning projects are the most important in hydraulic and hydrological issues and projects. The flood used to design structures and influenced by hydrological ...
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Introduction: Estimating the design flood of the basin for the design of hydraulic structures, stabilization of river banks, watersheds and flood zoning projects are the most important in hydraulic and hydrological issues and projects. The flood used to design structures and influenced by hydrological events is called design flood which depends on structure safety, cost, life expectancy, and possible damage. Intensity- duration- frequency (IDF) curves of rainfall is a hydrological tool for the estimation of the design flood and design of hydraulic structures. These curves are constructed for a region from rainfall data which are recorded at various continuations. Usually, in some countries such as Iran which has a large extent, there is not enough rain-gage station; or the length of the statistical period is low, so it is impossible to calculate the IDF curves. But since it is not usually possible to access daily rainfall data, the fractal theory can be used to estimate the precipitation data in different consistency and the IDF curve with a very good accuracy.
Materials and Methods: Korramabad river basin, one of sub-basin of Karkhe basin, often has been exposed to destructive floods and damages caused by it. In this research, the intensity-duration-frequency curves of the catchment area are estimated using fractal theory at first, and then the design precipitations are obtained in different return periods. In the next step we calibrated HEC-HMS rainfall- runoff model and finally the design floods are estimated in different return periods. The HEC-HMS model is an extension of the HEC-1 model under Windows, with all its capabilities. Hydrographs calculated by this model are used directly or in combination with other software for various purposes such as water supply, urban drainage, flood and flow forecasting, land use change, flood control studies and exploitation of reservoir systems.
In this research, SCS curve number method and recession method are used to calculate the losses and base flow. Also for estimation of runoff, SCS curve number, Snyder unit hydrograph and Clark unit hydrograph are used in three methods and after comparing the results of the three methods in the calibration stage of the model, the Clarke unit hydrograph method is identified as the best method for estimating runoff. Also the Maskingham method has also been used for flood routing. The data needed for this study include rain gage data, hydrometric data, physiographic data of the basin, and also amounts of CN or curve number of the basin. Rain gage and hydrometric station used in this research are Chamanjir station.
In this research, due to the importance of peak discharge for designing hydraulic structures, the optimization of the parameters has been done using the peak-weighted RMS Error criterion. In the calibration step, Comparison between hydrographs shows that there is a good agreement between computational and observational hydrographs, in such a way that the difference between the simulated and the actual peak discharge are 0.6, 0.2 percent for the selected floods. After calibration of the HEC-HMS rainfall runoff model for the studied area, this model is used to estimate the design flood. In the process of conversion precipitation to runoff, it is necessary to determine the pattern for temporal distribution of rainfall at the stations and in the area. To do so, the non-dimensional rainfall data are plotted for some storms with different time durations. For making data for each storm non-dimensional, the accumulated depth of precipitation to the desired time step was divided by the total depth of storm’s rainfall. The same procedure was carried out to make the time axis non-dimensional. By analyzing the precipitation data of the recorder station at the basin, it was found that in the majority of the precipitations, 20% of rainfall occurs in the first quarter, 20% in the second quarter, 40% in the third quarter and 20% in the fourth quarter.
Results and Discussion: The results of this research show that:
Daily precipitation data have a fractal characteristic in the ranging from 1 to 8 days, and during this time interval, rainfall data can be converted from a continuity to another continuity.
Due to the lack of recorded rainfall statistics in different continuations, using fractal method can be a useful way to prepare IDF curves in this basin and these curves are obtained based on the daily rainfall data available.
There is high efficiency of fractal model and HEC-HMS model in this catchment and the Gambel probabilistic distribution is appropriated for the maximum daily rainfall data of this basin.
Mohammad Reza Goodarzi; Alireza Faraji; Mahdi Komasi
Abstract
Introduction: Uncertainty estimation of climate change impacts has been given a lot of attention in the recent literature, However, uncertainty in downscaling methods have been given less attention. Today many studies have been done about the future impact of climate change on human life and water resources. ...
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Introduction: Uncertainty estimation of climate change impacts has been given a lot of attention in the recent literature, However, uncertainty in downscaling methods have been given less attention. Today many studies have been done about the future impact of climate change on human life and water resources. Urban development, water conflicts, and Green House Gases increasing will intensify this event in future and will alter rivers flow. Basin catchment has faced to flow recession and also runoff decreasing in few last decades. At this field the climate change effects will intensify this conditions in future decades too. The first step of climate change impacts studies is the projection of future climate variables (e.g precipitation and temperature). GCMS models and their outputs are useful tools for this projection. The main problem is the mismatch of spatial scale between the scale of global climate models and the resolution needed for impacts assessments.
Materials and Methods: The Gharesou River Basin is located in the west of Iran. Its area is approximately equal to 5793km2, and the maximum and minimum of its heights are 1237 and 3350 m, respectively. The average of annual rainfall varies from 300 to 800mm. This study focuses on various climate models from IPCC fourth and fifth reports and has been used two downscaling methods including the statistical and proportional downscaling methods and also scenarios and different climate models for considering different uncertainty. The new scenarios as Representative Concentration Pathways (RCPs) of greenhouse gasses have been used in fifth assessment reports (AR5) of IPCC. The Representative Concentration Pathways describe four different 21st-century pathways of greenhouse gas (GHG) emissions and atmospheric concentrations, air pollutant emissions and land use. The RCPs represent the range of GHG emissions. Different kinds of downscaling method include 1) Proportional downscaling that is adding coarse-scale climate changes to higher resolution observations (the delta approach); 2) Statistical method (eg SDSM model; CLIGEN; GEM; LARS-WG and etc); 3) Dynamical method that is application of regional climate model using global climate model boundary conditions (e.g, RegCM3; MM5 and PRECIS). statistical downscaling method processes establish relating large scale climate features (e.g., 500 MB heights), predictors, to local climate (e.g, daily, monthly temperature at a point), predictands. The SDSM software reduces the task of statistically downscaling daily weather series into seven discrete processes that are consist of quality control and data transformation; screening of predictor variables; model calibration; weather generation (observed predictors); statistical analyses; graphing model output and scenario generation (climate model predictors). HEC-HMS (Hydrologic Modeling System) has been designed by HEC (Hydrologic Engineering Center) for simulation of precipitation-runoff processes in a drainage basin. The HEC-HMS simulation methods represent - Watershed precipitation and evaporation: These describe the spatial and temporal distribution of rainfall on and evaporation from a watershed. - Runoff volume: These address questions about the volume of precipitation that falls on the watershed: How much infiltrates on pervious surfaces? How much runoff of the impervious surfaces? When does it run off? - Direct runoff: including overland flow and interflow. These methods describe what happens as water that has not infiltrated or been stored on the watershed moves over or just beneath the watershed surface. Baseflow: simulate the slow subsurface drainage of water from a hydrologic system into the watershed’s channels.- Channel flow: These so-called routing methods simulate one-dimensional open channel flow, thus predicting time series of downstream flow, stage, or velocity, given upstream hydrographs. HEC-HMS includes several models for calculation of cumulative precipitation losses but only the SMA module is continuous (a module that simulates the losses for both wet and dry weather conditions). Other loss models are event based.
Results and Discussion: The results of criteria and models weighting show that CANESM2 and HADCM3 are better than other models for future temperature and precipitation projection for statistical downscaling and HADCM3 for future precipitation and HADGEM for future temperature assessment for Proportional downscaling. According to various scenarios, future temperature and precipitation projection (2040-2069 period for the statistical and 2040-2052 period for Proportional downscaling) have downscaled and have given to HEC-HMS model for future flow projection. Already the rainfall-runoff model has calibrated and validated base on observed flow data in reference period that daily coefficient of determine was 0.7 for calibrated period and 0.6 for validated period. Finally, flow variation has investigated that Most of GCMS represent increases in winter flows and reductions in other season flows.
Mohammad Reza Khaleghi; Vahid Gholami; Ghorbanali Khodabakhshi
Abstract
Introduction: In the last century, dams have constructed with the objective of water supplies for agriculture, drinking water and industry. However, the results from the performance review of dams show adverse effects on the downstream environment and the availability of water resources. The purpose ...
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Introduction: In the last century, dams have constructed with the objective of water supplies for agriculture, drinking water and industry. However, the results from the performance review of dams show adverse effects on the downstream environment and the availability of water resources. The purpose of the Chashm dam construction on the TalarRiver's tributaries is the water supply for Semnan city.
Materials and Methods: This study was conducted in TalarRiver watershed. TalarRiveroriginatesfrom AlborzMountains in Mazandaran province, in the southern Caspian Sea basin, in north of Iran and flows parallel with the Firouzkooh-Ghaemshahr road and it arrives to the Caspian beach area in the Malek Kala village. In order to supply the water requirements of Semnan city, the construction of Chashm dam on the TalarRiver's tributaries placed on the agenda of the Ministry of Energy. However, because of the uncontrolled exploitation of agricultural streams and invasion of privacy riverbed, the TalarRiver has acute and critical conditions from the point of hydrologic and environmental. To study the hydrological impacts of Chashm dam, Talar watershed was considered with an area of approximately 1057 square kilometers of the Pole Sefid gauging station using a rainfall-runoff model.
Results and Discussion: Simulation of the study area hydrological behavior shows that the Chashm Dam average water discharge is near to 8.6 million m3. This figure will be significant changes during wet and droughtperiods. The minimum and maximum monthly discharge of the Chashm Dam watershed in August and February is equal to 0.31 and 0.55 m3/s respectively. The minimum and maximum monthly water demand in turn in October and August is equal to 0.015 and 0.4 m3/s respectively and this shows that the river discharge in June is lower than the downstream water demand. Based on confirmed studies of the Kamandab Consulting Engineers, drinking water requirement of Semnan province, water rights users' requirement and downstream environmental requirements are 4.54, 2.164 and 2.448 million m3, respectively. This is despite the fact that the volume of annual input water is slightly lower than this figure in normal.
Conclusion: Simulation of the study area hydrological behavior shows that the Chashm Dam average water discharge is near to 8.6 million m3. This figure will be significant changes during wet and drought periods. The minimum and maximum monthly discharge of the Chashm Dam watershed in August and February is equal to 0.31 and 0.55 m3/s respectively. The minimum and maximum monthly water demand in turn in October and August is equal to 0.015 and 0.4 m3/s respectively, and this shows that the river discharge in June is lower than the downstream water demand. Based on confirmed studies of the Kamandab Consulting Engineers, drinking water requirement of Semnan province, water rights users' requirement and downstream environmental requirements are 4.54, 2.164 and 2.448 million m3, respectively. This is despite the fact that the volume of annual input water is slightly lower than this figure in normal. In addition, the Chashm Dam area is about 110 hectares and given the minimum annual actual evaporation equal to 700 mm, about seven hundred thousand cubic meters of water stored in the reservoir will be lost. Due to the simultaneous occurrence of the maximum water requirement, maximum evaporation and a minimum of water inlet to the Chashm Dam reservoir in warm seasons, it seemsthat, it is not possible to provide needs based on these studies and no doubt, in the case of water supply in Semnan province, we have to stop the flow of the river in downstream of the dam. The results of this study suggest that on many rivers large headwater dams have reduced the frequency and duration of floodplain inundation downstream and these changes lead to changes in downstream ecosystems. The results from the simulation and analysis of the Chashm Dam in downstream are as follows: a) stop of the river flow in downstream of the dam site, b) the sharp decline in river discharge in minimum (varied) flows, c) reduce in the rate and volume of maximum flows, d) changes in the hydrological regime of the river such as base flow, flow stop, the frequency of the river full section and competency which will make dramatic changes in the morphology of the river and downstream ecosystems. Note that is not verified by modeling and forecasting studies, is how to manage the reservoir. The amount of water stored in the reservoir and discharge to downstream is directly a function of the reservoir management.
