Iranian Water Research Journal

Abstract

Abstract Accuracy in water flow measurement is always considered as one of the most important issues in water resources management. Bed and wall sediment of alluvial rivers transfer in watershed and after entry into channels, the sediment deposit behind flow measurement structure and therefore, influence their performance. Weirs are widely used to measure discharges. In excellent installations, they provide accurate measurements of discharge over a wide range of flows with a constant discharge coefficient. However, many weirs around the world are filled with sediment and require manual rating curve adjustments or dredging. Including flow measurement structures is V-notch crested weir that is more accurate because of higher sensitivity in the flow depth measurement. The relationships that have already been presented according to experimental results for discharge coefficient has been extracted and developed in without-sediment conditions.
In the present study, effect of sedimentation level and weir angle on discharge coefficient in v-notch weir was investigated, experimentally. Parameters included: flow discharge, weir angle, weir height, channel slope, and degree of sedimentation were varied. All tests have been performed by taking six weir angles (75, 90, 105, 120, 130 and 140 degree) and three weir heights which were appropriate with every angle. Four sedimentation levels consisted of no-sediment bed and the sediment levels set to one-third, two-thirds and equal to the height of the weirs. Also, four bed slops were considered as: 0, 0.8, 1.6 and 2.4%. The experiments were performed in the University of Tarbiat Modares water structures laboratory. The flume used with dimensions of 10 m in length, 0.3 m in wide, 0.4 m in height, and adjustable slope was varied from -1.5 to 2.5 percent. Framed walls were constructed with glass. The flume was equipped with a measurement traverse. Discharge rang was from 0.3 to 16.3 L s-1. In all tests weirs installed in middle of flume long (5 m after flume entrance). Sedimentation was simulated by placing coarse gravel with 2 cm diameter in an area within 1 m of the weir and at an elevation equal to the invert of the weir. In all tests, the material did not move during the experiment. For the given geometrical condition (weir angle, weir height, bed slope and degree of sedimentation), the flume was first filled with water up to the elevation exactly equal to the invert of the weir. Afterward the flow was decreased to each target value using Electro Magnetic flow meter with ±5 percent accuracy, then water level measured with point gauge that its accuracy was 0.1 mm. Approximately in each experience 12 data collected of water levels and flow discharge. Measuring of water surface elevation was repeated for statistical inference of the effect of turbulent unsteadiness on discharge measurements.
Test results indicated that increase in the weir angle, increased the discharge coefficient for all weir heights and slopes, but increase in the weir height, caused to decrease the discharge coefficient. Comparing result between the sedimentation degree and discharge coefficient indicated that increase in the sediment level, leaded to increase the discharge coefficient. Also, a direct relationship between the discharge coefficient and bed slope was observed so that the maximum discrepancy of the discharge coefficient in without and full sediment condition was related to 140 degrees weir angle and in 2.4 percent flow bed slope, which was equal to 14.8 percent. Also, the results showed that an increase in the ratio of upstream water depth to the weir height (H/P), leaded to an increase in the discharge coefficient for all experiments. These results were favorably acceptable comparing with other studies.
Ultimately, according to the experimental data, and by using SPSS software, also formation of non-linear regression, the non-dimension equation has been suggested in order to estimate discharge coefficient in v-notch weir. The equation resulted in a high correlation coefficient (R2=0.956) for discharge coefficient estimated angle, weir height, flow bed slope and sediment level. By comparing between calculated values of the discharge coefficient of suggested equation and laboratory measurement values for calibration data and validation data considering ±5 percent of the levels error observed that suggested equation has high accuracy for calculating the flow discharge. In the following, the present study suggests investigating the effect of sedimentation level on discharge coefficient in other weirs for further researches.

Abstract

Abstract Considerable amount of water in irrigation practices drain out due to it uses much more than crop water requirement. Agricultural wastewaters are the most important reuse sources because of extremely high amount. Therefore, using of these resources is crucial in Iran because of shortage water resources. One of the drainage water reuse strategies is treating by biological filters. The cheap adsorbents materials, especially agronomical waste matters, can have good potential for treating and building suitable condition in environmental asspect (Niknam et al., 2014). These materials are such as rice bran, wood sawdust, wood charcoal, pressed tea, walnut shell, peanut skin and others, based on availability in the experimental area. These natural adsorbents have the ability to adsorb metal ions due to different functional groups present on their macromolecules (Tarley et al., 2004). The first research was conducted on metal absorption by using of different organic waste and xylem vessels by examining the removal of mercury (Friedman and Waiss, 1972). The other researches were done by (Bina et al., 2003) in removing heavy metal and (Abdel-Ghani et al., 2007) in removing Pb. Masri et al. (1974) used Yew skin for absorbing of the soluble ions like mercury, Pb and cadmium. Based on results, the most absorption was considered in mercury. Nowadays, there is much attention to use of natural materials with ability of absorbing contamination such as heavy metals. The use of rice husks as a natural solid adsorbent of trace metal for Cd and Pb was studied by (Tarley et al., 2004). The results showed that modified rice husks with 0.75 mol l-1 NaOH solution had more adsorption rate than natural rice husks. In last years, the amount of water supply in Guilan province has decreased due to constructing dams in upstream of Sepidrud River, so it is important and necessary to find new resources. On the other hand, due to low efficiency of irrigation in this area, the high amount of water is discharged as runoff and drain water. Therefore, reusing of drainage water is the best solution for overcoming the water scarcity. The purpose of this study was to investigate the effect of four types of bio-filters including wood sawdust, rice bran, wood charcoal and pressed tea on treating of Nitrate, Magnesium, Sodium, pH and EC in agricultural drain water.
Experiments were conducted on paddy fields drainage water in Astaneh town, Guilan province, Iran. First, four basins were dug in side of main drain by using of trenchers with 1 m×2.5 m×20 m sizes and 2% gradually slope. After that, the bottom and sidewall of basins were covered with thick plastics to prevent water seepage. At the end of each basin, drain tubes in shape of T were used to control drainage water. The thickness of applied bio-filter materials in each basin (including wood sawdust, rice bran, wood charcoal and pressed tea) was 80 cm, and mineral envelop was applied above the bio-filters to fix them and prevent of damage. Then, the pump was installed next to the basinsfor irrigating. The schedule of pump was 22 hrs working in a day night and 2 hrs resting, and the amount of pumpage was determined by saturated hydraulic conductivity of materials. During summer, rice growing season, 8 times and during autumn, 11 times was sampled of outlet water of bio-filters, so overall these were 19 samples. The parameters such as N, Mg, Na, pH and EC in the samples were determined in laboratory of Guilan regional water company. The statistical analysis of T paired in SPSS software was used to determine significance differences among samples.
The results demonstrated that all bio-filters had significant effect on filtering of some parameters in the drain water investigated in this study. This was due to the concentration of pollutants. All bio-filters decreased the pH of water. The pressed tea was not good in decreasing the pollutants, although rice bran and wood charcoal were a little effective in that. This result can be due to the low amount of contamination in drainage water, in some experiences. Also, the wood charcoal decreased the amount of N, significantly. However, sawdust bio-filter had positive effect in decreasing of EC, pH, N and Na, and had better results than the other filters. In addition, this bio-filter decreased N in outlet water by 0.7 mg lit-1. Therefore, the role of sawdust bio-filter in biological processes of drain water should deserve more attention.

Abstract Increasing water efficiency and productivity is one of the most important and effective ways to tackle the water crisis and mitigate the effects of drought in agriculture (Hajari-Georgi, 2007). Operation of irrigation (time and depth of water) is determined based on the amount of plant water need. Therefore, to increase the efficiency of irrigationthe crop water requirements have to be precisely estimated. Appropriate management of irrigation water requirements of plants can be achived based on accurate estimates (Farshi and et al., 2003). Among the reasons of errors in estimating crop water requirements are the lack of knowledge of, irrigation designers in agroeconomical issuesand plant physiological characteristics in relation to water consumption and alsochoosing unsuitable methods for estimateing crop water requirements (shahabi and et al, 1383). In drip irrigation systems, local soil or only a portion around the roots of the plants are wet. Irrigation systems and irrigation scheduling can affect water uptake by plants (Michlakis and et al.1996). Using both methods of monitoring soil moisture and weather data simultaneously is needed to estimate the amount of plant needs and irrigation water.
This study used the local irrigation system (bubbler) by monitoring soil moisture and meteorological data to calculate the water requirement of two cultivars of pomegranates (Yazdi and Saveh) and the effect of different irrigation regimes on yield during the growing season. Production in the gardens of four-year pomegranate was examined. Plan was designed on the area of one hectare with sandy loam soil, in a factorial experiment based on randomized complete block It was concluded three treatments (I1, I2, I3), respectively, full irrigation (FC), 25 percent deficit irrigation and 50 percent deficit irrigation, in three replications. Meteorological data required were gained from long-term statistics of synoptic stations weather of Yazd. Evapotranspiration was estimated by Penman-Monteith CropWatt software and calculated during the experiments and their average was used in this study.
In order to analyze and determine the amount of irrigation water and regime in each period, the volumetric soil moisture content by means of reflection from the waves TDR (Model TRIME_FM) were measured.
The amount of water consumed at the end of the growing season in each irrigation regimewas calculated as 3744.44, 2783.1 and 1873.1 cubic meters of water per hectare, respectively for three levels of irrigation (I1, I2, I3). Vriation range in the water need during the growing season was 0.6 to 2.43 mm per day, (I1). Analysis of variance showed that the yield of irrigation regimes I1 and I2 with I3 were significantly different at 5% level. Given the amount of evapotranspiration in each irrigation regime, crop coefficients (Kc) for I1, I2, I3, were 0.54, 0.4 and 0.27, respectively.
According to the results of irrigation water applied to four-year mature trees and trees in full irrigation can be concluded that the age level of the canopy is an important issue in determining the water requirements of the tree. The results showed that the amount of water consumed by fouryear trees comparing to mature trees during the growing season in FC treatments reduce about 6000 cubic meters. Canopy of trees acoording to their age is important in predicting the amount of water used in each of the regimes and causes a large difference in the rate of evapotranspiration. The results showed that with the increase in soil moisture or too much irrigation, the evapotranspiration increased. This reflects the fact that although the pomegranate tree is drought- tolerant, itrequires sufficient water for optimum growth. The lower Kc represents less growth, andsmaller canopy and therefore less amount of ET. The amount of Kc over the growth years shows the sensitivity of the irrigation water requiremen. Pomegranate is a defoliant fruit tree, which has germination and emergence in the spring and leaves fall in the winter. Also, the amount of Kc is very different from season to season (bantana and et al 2010). Changes in water treated in I1 during the growing season were from 0.6 to 2.43 mm per day. The results of variance analysis showed that irrigation levels of I1 and I2 at 5% level had a significant difference with I3. Fainally, due to the lack of water resources, investigating impacts of defecit irrigation in different growth stages is recommended.

Abstract Meandering rivers are among the most dynamic features on earth's surface. A meandering river exhibits progressive change in position as it migrates across its floodplain. The planform dynamics of meandering rivers result from the interactions among flow, sediment transport, and evolving channel morphology that collectively scale with planform curvature. The view that planform curvature has a major influence on the rate and character of meander migration is supported by field observations and theoretical considerations. Morphological river changes (bed topography and/or plane-shape changes) occur as result of natural and/or of human interventions so that alluvial meandering streams strive to achieve an equilibrium configuration. As documented by many experimental and theoretical works the plane shape of a meander wave is the result of the complex interplay flow pattern-bed deformation bank erosion. The geometric shape of the meander wave gives rise to a complicated flow field which, in turn, modifies the bed topography and reshapes the meander wave through the bank erosion. In fact, in nature, different meandering streams exhibit different geometric characteristics so that the stream conditions may vary from one meander loop to another. Thus, many laboratory and field studies, apart numerical researches show that the evolution of a meander wave is mainly governed by the bed deformation that drives the erosion process at the channel banks. Particularly, outer-banks are considerably vulnerable to erosion processes. On the other side, the evaluation of the bank erosion and the consequent migration of meandering rivers are fundamental, both because of hazards associated with them and because of their effects in riparian ecosystem dynamics.
The modeling of meandering-river migration requires the simulation of the following processes: hydrodynamics, sediment transport, bed morphodynamics, and bank erosion. Furthermore, in this paper plane form of a meander wave was determined by the mathematical model. Under the conditions prevailing in natural streams, the channel centerlines follow sine-generated curves, with an assumed steady-state turbulent and subcritical flow, of large width-to-depth ratio and small Froude number. The plane deformation of the channel was caused by the action on the banks of the convective vertically-averaged meandering flow. It has to be pointed out and as it is well known that, the regime development of the flow width goes much faster than that of the channel slope. Therefore, in this model the regime development of slope (i.e., the loop expansion), a nearly constant flow width was assumed, which can be identified as the regime width. Accordingly, in this article, the flow width (with as the flow depth) was assumed to be constant along the channel length. Since the width-to-depth ratio was large, the effect of the cross-circulation was negligible. In overall, the channel deformation, as the result of both channel down valley migration and lateral expansion, is entirely due to the action of the convective vertically-averaged meandering flow. The growth (expansion and expansion) of meander loops is attributed to the regime-trend the loops continually grow in their amplitude (i.e., their length increases) and thus the channel slope progressively decreases to the regime state. This model was able to predict the migration and expansion of meander loops.
The following computational procedure was adopted to determine the migration and expansion speed of the meander loop under various values of the deflection angle along the channel centerline. (1) Set regime channel conditions, (2) Compute of meandering channel lengths, (3) Calculate regime slope, (4) Compute water depth, (5) Compute the average specific volumetric sediment transport rate (sediment transport is assumed to be the only bed-load in this article), (6) Compute the angle between the streamline and the coordinate line, (7) Compute the migration speed of meander loops and (8) Compute the expansion speed of meander Loops. The model was then applied to a sine-generated meandering channel and the migration and expansion component of bank speed deformation was calculated. Modeling results showed that, for small deflection angle migration was the main deformation in the meandering channels, on the other hand, for large deflection angles both migration and expansion became smaller in the meandering channels. Furthermore the effect of deflection angle along the channel centerline and channel-averaged specific volumetric sediment transport rate, have been proposed by model. The result showed that the specific volumetric sediment transport rate had significant effect on channel migration and expansion rates.

Abstract According to the water crisis and the need for careful planning, prediction of potential evapotranspiration can be helpful to plan water resources and adopt appropriate management methods. Furthermore, knowing the exact amount of evapotranspiration is essential for estimation of water use and irrigation system design. Different models have been provided by researchers for estimation of evapotranspiration, which vary considerably from each other in terms of the number of meteorological parameters they take into account. But due to the lack of the reliable long-term data in some stations, use of model with little data is needed and will be necessary to help planners. In this study the Simulation of Evapotranspiration of Applied Water model (SIMETAW) was evaluated for generation of daily weather data from the long-term monthly values of four synoptic stations (Rasht: Very wet, Shahrekord: Semi-arid, Ahvaz: Arid and Sanandaj: Moderate), also estimation of potential evapotranspiration in the base period (1961-2000) and future period (2040–2080). In the first stage, SIMETAW model was run using long-term average monthly weather data in the base period and daily weather output data were obtained for 41 years. Then by using this data, long-term daily values were calculated and compared with observed data. To compare the results, Coefficient of Determination (R2), Root Mean Square Error (RMSE) and Index of Agreement (d) was used.
The results showed that the model simulations in all stations had acceptable accuracy and the highest accuracy of model in simulation of maximum temperature (R2=0.9954) and precipitation (R2=0.3716) related to Mediterranean climate, minimum temperature (R2=0.9947) and dew point temperature (R2=0.9942) related to very wet climate, wind speed (R2=0.8094) related to arid climate and solar radiation (R2=0.9902) related to semi-arid climate. The accuracy of the model for simulation of rainfall in four stations was low (R2=0.2457, R2=0.2435, R2=0.3553 and R2=0.3716 for arid, very wet, semi-arid and Mediterranean climate, respectively). The highest accuracy of SIMETAW model in simulation of evapotranspiration was belong to mediterranean climate (R2=0.9936), semi-arid climate (R2=0.9935), arid climate (R2=0.9903) and very wet climate (R2=0.9846), respectively. In the second stage, meteorological parameters were simulated in future period (2040-2080) under two emission scenarios (A2 and B2) by HadCM3 (Hadley Centre Coupled Model, version 3) outputs and using downscaling model of SDSM) Statistical Downscaling Model(. To verify the accuracy of SDSM model in downscaling outputs of HadCM3, long-term average of daily data in the base period 2001-1961 were compared with simulated data using the SDSM in the future period. The results showed the high accuracy in simulation of all parameters. Comparing data from downscaling in the future and observed data in the base period, showed that in four stations, in total, maximum temperature, minimum temperature, dew point temperature and wind speed will increase in the future period compared to the base period while rainfall will decrease. For example, in Ahvaz station, the average increase in the future maximum temperature, minimum temperature, wind speed and dew point temperature will be equal to 3.4, 8.0, 5.0 and 18.9 percent under the A2 scenario and 2.1, 5.7, 5.0 and 14.7 percent under the B2 scenario, respectively. Also, the average decrease in the future rainfall will be equal to 17.9 percent under the A2 scenario and 20.5 percent under the B2 scenario, respectively.
In the third stage, from SDSM model outputs in the future period, long-term monthly values were prepared and used as SIMETAW model input. Then from this data, long-term monthly values were produced and then compared with SIMETAW model outputs in the base period. It was found that in four stations, in total, the potential evapotranspiration will be increased under the A2 and B2 compared to the base period. The average increase in the future potential evapotranspiration will be equal to 10.4, 9.5, 10.7 and 4.3 percent under the A2 scenario and 10.3, 8.8, 9.4 and 2.9 percent under the B2 scenario, respectively, in Mediterranean, dry, very wet and semi-arid climate. Given the high correlation between simulated and recorded values, it can be concluded that SIMETAW model can be applied effectively and efficiently with high accuracy for simulation of weather data, potential evapotranspiration and also filling gaps in four stations. Also, this model can be used as an appropriate tool for irrigation engineers and decision makers to predict irrigation needs, using monthly records when daily data is not available.

Abstract

Abstract River flow investigation is one of the main issues in hydrology and water resources studies. Chaos analyses can be used to analyze the river flow time series as a dynamic system with highly sensitive to initial conditions. The chaos theory, which is based on non-linear dynamic systems, has resulted in a great change in understanding and expressing different phenomena. This theory deals with the study of systems that at first glance may seem irregular; but in fact they are governed by clear rules. Such systems are very sensitive to initial conditions, such that minor inputs could have significant impacts. Since investigating the presence of different characteristics at different time-scales in rivers is one of the main challenges of hydrology, the aim of this paper was to study the behavior of river flow process at different time scales. Despite chaotic studies conducted on river-flow discharges, these analysis of Dez River discharge, located in southwest of Iran, has not been implemented for different time scales. In this study, based on the flow-discharge data of Bamdezh station on Dez River, the presence of chaos in daily, monthly and seasonal scales is discussed.
Dez River consists of two main branches, namely Sezar and Bakhtiari, and after exiting from the mountainous region in the north of Andimeshk and Dezful cities, enters into the Khuzestan plain. After passing the city of Dezful, and running through a 186 km meandering path (from Dezful to Band-e Ghir), it joins Shotait and Gargar Rivers in Band-e Ghir and forms Great Karun River, which flows toward city of Ahvaz. Bamdezh is the last hydrometric station on Dez River, before joining the great Karun River. Daily and monthly discharge data of Bamdezh station during 31 water-years (1981 to 2011) were used. Four non-linear dynamic fallowing methods were used: 1) phase space reconstruction, 2) correlation dimension method, 3) determination the greatest Lyapunov exponent and 4) calculation the Hurst exponent. The state (phase) space is a useful tool to study the dynamic systems. According to this concept, a dynamic system can be described by means of a state space diagram. Each dynamic system consisted of differential equations with partial derivatives. To determine these equations and their type, the embedding dimension and delay time parameters have to be determined. The delay time could be obtained from the method of assessment of correlation function (ACF) or average mutual information (AMI). In this study, the average mutual information method was used to estimate delay time. In this method, time of the occurrence of first minimum in the average mutual information function is selected as the appropriate delay time. The embedding dimension is obtained from the false nearest neighbor (FNN) method.
The obtained results showed that delay time for daily, monthly and seasonal time-scales is 80 days, 2 months and 2 seasons, respectively, and optimal embedding dimension is 10, 3 and 1, respectively. The correlation dimension was calculated to determine the chaotic nature of the system. Results revealed that correlation dimension at daily and monthly scales, due to saturation of the diagram, was 3.765 and 3.84, respectively. Therefore, Dez River system is chaotic in these two time scales. But at the seasonal time scale, the diagram trend was ascending and as a result the river discharge is random. Another indicative criterion of the chaotic system is the greatest Lyapunov exponent. By using this exponent, the behavior could be determined in each dimension; positive Lyapunov exponent is an important indicator of a chaotic system. In this study, the greatest Lyapunov exponent was calculated on the basis of proposed Rosenstein method. By having the value of optimal embedding dimension, this exponent is calculated. In the case of no optimal embedding dimension, this value is predicted. At the daily and monthly time scales, positive greatest Lyapunov exponent (0.0149 and 0.0373) was obtained.
Hurst exponent is based on his studies on river data obtained from different time periods. By using this exponent, the presence of non-periodic variations in river water flow could be realized. Hurst showed that if the exponent is equal to 0.5, it indicates an independent and completely random process; if 1> H> 0.5, it implies a continuous time series with very long memory; finally, if 0.5 > H> 0, it indicates that the process is not continuous. Based on the obtained results at daily and monthly scales, this exponent was 0.7556 and 0.7773, respectively, for Dez River discharge, and both confirm that the river behavior is chaotic at these two time scales. Besides, the Hurst exponent in a random process may be obtained as positive. Therefore, this river’s discharge can be predicted at daily and monthly scale. Moreover, at seasonal time scale, due to lack of correlation dimension, the flow behavior was shown to be random.

Abstract Recent human activities have raised average temperature of the Earth’s surface. This increase will also influence climate variables and will result in climate change. With changing climate variables such as temperature and precipitation, the hydrologic regime of the rivers, and consequently flood frequency and magnitude, will also change (IPCC, 2001; Khazaei at al., 2012). For active adaptation strategy, it is necessary to assess impacts of climate change on floods. It is frequently mentioned in the literature that one of the potential impacts of climate change is the change on floods, however limited studies aimed at investigation of the change of flood regime due to CC. Generally, climate change impact assessment on floods comprises two main steps: preparing future climate data and hydrological simulation of river-flow. For hydrological simulation of flood flows, hydrologic models can be classified in two main classes, including single-event models and continuous models. In some studies, single-event rainfall-runoff models have been used (e.g. Roy et al., 2001; Muzik, 2002). In such studies, the reason for using these models was simplicity. In spite of the ease in using single-event models, the initial soil moisture condition in the future changed condition is unknown. Due to high sensitivity of simulated floods to initial condition of soil moisture, application of single-event models deals with great uncertainty (Roy et al., 2001). So, for assessment of climate change impact on floods, continuous models are required (Prudhomme et al., 2002). For climate change impact assessment on floods using continuous hydrologic models, normally, watershed-scale time series with fine time step for future climate are needed (Prudhomme et al., 2003). The most common tools to simulate future climate scenarios are GCMs. However, since resolution of GCM outputs is course, it is necessary that GCM outputs be downscaled. At least, rainfall and temperature data should be downscaled for continuous hydrologic simulation, throughout it is important to preserve the correlation between the downscaled variables (Fowler et al., 2007). Among downscaling methods, Change Factors (CFs), Weather Generators (WGs), and RCMs preserve the correlation between downscaled variables. In general, RCMs and WGs cannot accurately reproduce extremes. So in most previous studies CFs method have been used (e.g. Reynard et al., 2001; Prudhomme et al., 2002, 2003; Mareuil et al, 2007; and Kay et al., 2009).
In this paper, the climate change impacts on floods were assessed in one of the main sub-basins of the Karun basin. Rainfall-runoff process of the basin was simulated using ARNO semi-distributed continuous rainfall-runoff model (Todini 1988). The main phenomena which represented in the ARNO model are: snow melt, water losses through evapotranspiration, soil moisture balance, groundwater flow, overland and channel flow routing. The rainfall-runoff model was calibrated and validated for the basin using eight years of high-quality daily data of stream-flow at the outlet, and daily precipitation, Tmax, and Tmin at Yasuj meteorological station, close to the centroid of the basin. For future climate scenarios, projections of the CGCM3 model under A2, A1B and B1 emission scenarios were used for both control (1974–2000) and future (2067–2093) periods. The climate scenarios were downscaled for the basin using the Change Factors (CFs) method. In CFs method, the differences between means of GCM outputs for control and future periods are applied to every baseline observed data series, either as summation (for temperature) or multiplication (for precipitation).
As result of rainfall- runoff modeling, the Efficiency Criterion (EC) of calibration and validation stages were turned out to be 0.87 and 0.83, respectively, also determination coefficients (R2) were 0.85 and 0.88, respectively; while the flood values were simulated closely. In comparison with other studies, Zhang and Savenije (2005) adopted acceptable calibration when EC is greater than 0.6. Meanwhile, Kamali et al. (2007) accepted EC values of greater than 0.7. Thus, the performance of the model in overall the hydrograph is very good. In order to produce future climate series, the CGCM3 projections for each of the A2, B1 and A1B scenarios were downscaled for the basin. With the future climate data and the rainfall-runoff model, daily stream-flow series at the future period were generated. Annual maxima daily floods were extracted from the daily stream-flow series and climate change impacts assessed on annual maximum floods distribution. Based on the results, the magnitude of the floods will increase in the changed future climate. For instance, under these scenarios, flood magnitude with a return period of 25 years will increase between 50% and 120% for period of 2067–2093, in comparison to 1974–2000 historic period. Also, flood magnitude with a return period of 100 years will increase between 54% and 126%, under B1, A1B, A2 scenarios. It is concluded that despite the magnitude of the change, which is upon the choice of the emission scenario, the climate change will impose considerable increase on floods under all the regarded scenarios.

Abstract

Abstract