R. Chamani; M. Azari
Abstract
Introduction: Over the past decades, millions of hectares of high-quality lands have been converted to other uses and low-yielding agriculture, which have had some unpleasant consequences for watershed hydrology. Analysis of hydrological responses of different basins to land use change has shown that ...
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Introduction: Over the past decades, millions of hectares of high-quality lands have been converted to other uses and low-yielding agriculture, which have had some unpleasant consequences for watershed hydrology. Analysis of hydrological responses of different basins to land use change has shown that correct land use balances the hydrological status of the basin, so that land use and the type and density of vegetation play an effective role in permeability and runoff reduction by changing humidity, soil organic materials and soil structure. Dimensions of hydrological effects of land capability in Chehel chay watershed in Golestan province, which is affected by land use change and deforestation, are more important. Therefore, this study seeks to investigate different scenarios of land use change and its effect on the hydrological status of the basin.
Materials and Methods: The J2000 hydrology model was used to simulate the hydrology of the basin. To better investigate the spatial and temporal variations of the hydrological parameters of the study area, it is divided into 2013 hydrological response units. After calibrating the J2000 hydrological model, the model was fed by rainfall data (1992-2014) and land use potential.
Results and Discussion: To evaluate the performance of the model, the dataset obtained in the time period of 2002-2014 was used for selection simulation and the first nine-years was considered as the calibration period and the remaining was considered as the validation period. The R2 of 0.67 and 0.55, and NAS coefficients of 0.83 and 0.76 were found in the calibration and validation periods, respectively. According to the ranking of Moriasi et al., the model efficiency is "good" and can be used in the present study. Several studies with similar observational data have reported similar results. The results showed that in summer and in May and June, the emptiest space in LPS soil pores is 3.07 and 3.21%, respectively. Increasing the consumption of MPS soil pores has also increased, and from 0.5 to 1.69% of the empty pores in the average soil pores has increased in these months. Therefore, increasing water storage in LPS pores in the months of May to June, surface runoff (RD1) decreased within the range of 6.28-26.38%, and the range of subsurface runoff (RD2) reduction was 4.41-8.41%. The amount of water percolation into groundwater aquifers was positive, and the highest infiltration into groundwater ranged from 0.83 to 1.72% for fast section groundwater (RG1), and from 0.48 to 0.52% for groundwater. Large pores do not hold much water, and water is transferred vertically to medium pores under gravity. When medium pores are saturated with water, water does not penetrate into these pores and remains in large pores and moves horizontally, increasing the subsurface flow. The results indicate that deforestation in order to expand agricultural lands and inappropriate use of the lands are the most important problems. Moreover, population growth has exacerbated the condition, necessitating proper land use management and planning. The scholars have also stated that proper land use has important effects on the water balance of watersheds.
Conclusion: In this study, the hydrological effects of land uses on the hydrological situation in Chehel chay watershed have been evaluated by simulations of the hydrological model. Our results reveal that the unplanned land use changes, land clearing, and expansion of agricultural lands have intensified the hydrological situation of the basin. The peak discharge of surface and subsurface runoff in hydrological response units decreased and the rate of water infiltration into soil and groundwater increased. Reduction of surface and subsurface runoff has also decreased the discharge in the basin outlet.
Farzaneh Naseri; mahmood azari; Mohamad Taghi Dastoorani
Abstract
Introduction: Determining the amount of watershed sedimentation and its spatial distribution by using field measurements in practice faces a serious challenge. In recent decades, hydrological models have been widely used by hydrologists and water resource managers as a tool for analysing water resource ...
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Introduction: Determining the amount of watershed sedimentation and its spatial distribution by using field measurements in practice faces a serious challenge. In recent decades, hydrological models have been widely used by hydrologists and water resource managers as a tool for analysing water resource management systems. The SWAT model is one of the semi-physical and semi-distributed hydrological models that have been widely used in recent years. Despite the wide use of the SWAT, simulation of the sediment has been associated with a large error in comparison to flow. These errors may come from using empirical methods such as the sediment rating curve for estimating sediment based on measured data. Therefore, in this research, the capabilities of the genetic algorithm (GA) were used to optimize the relationship between discharge and sediment and further optimal equation used for calibration and validation of the model.
Materials and Methods: The studied area is Fariman dam watershed with an area of 278.8 km2 which is located at latitude of 35 ˚ 33' to 35˚ 41' and longitude of 59 ˚ 34' to 59 ˚ 44' in Razavi Khorasan province. In this study, SWAT model was used to simulate runoff and sediment yield of Fariman dam watershed. In order to run the model, meteorological and hydrometric data including daily rainfall and maximum and minimum temperatures and sediment yield and discharge data, soil and land use maps of the watershed were achieved from relevant resources. The capabilities of the genetic algorithm were used to optimize the discharge -sediment relationship and were compared with sediment rating curve. For this purpose, optimization problem was defined for the genetic algorithm in MATLAB software as a search space of continuous values of the discharge –sediment coefficients. After that, sediment yield was extracted based on discharge data and calculated monthly sediment for SWAT calibration and validation. Sensitivity analysis, calibration and validation of the model were performed using the SUFI-2 algorithm using SWAT-CUP software. For this purpose using high sensitive parameters, the model was calibrated and validated for the period of 1991 to 2000.
Results and Discussion: Optimal coefficients extracted by GA indicate a better performance of the genetic algorithm in estimating the sediment yield. The comparative results of the sediment estimation models, revealed better performance of the genetic algorithm with RMSE = 70.9, NSE =0.46 and R2= 0.72 than the sediment rating curve. According to senetivity analysis of SWAT model, twelve parameters for stream flow and seven parameters for sediment yield were found to be sensitive. The most sensitive parameters for stream flow were SCS runoff curve number (CN2), effective hydraulic conductivity in tributary channel (CH_K1) and base flow alpha factor for bank storage (ALPHA_BNK) and the most sensitive parameters for sediment yield were peak rate adjustment factor for sediment routing, USLE equation soil erodibility factor (USLE_K), sediment concentration in lateral flow and groundwater flow (LAT_SED) and exponent parameter for calculating sediment reentrained in channel sediment routing (SPEXP). The SWAT calibration and validation results showed that the Nash-Sutcliffe efficiency index for monthly sediment and discharge for calibration period was 0.75 and 0.73, respectively and in the validation period was 0.85 and 0.76, respectively. Calibration and validation of the SWAT model was done with genetic algorithm model as an optimal method for deriving sediment data from measured daily discharge. The Nash-Sutcliffe efficiency coefficient for monthly discharge was 0.75 and 0.85 in the calibration and validation periods. Nash-Sutcliffe efficiency coefficients for monthly sediment yield were 0.86 and 0.81 for the same periods. SWAT evaluation results indicate that the model simulation is acceptable for predicting sediment yield and river flow. The performance of SWAT model in predicting of sediment in low flow is poor, which can be due to the effect of the parameters and model simplifications in the simulation of the sediment load.
Conclusions: In this research, simulation of runoff and sediment flow for Fariman dam watershed was performed using SWAT model. For this purpose, the capabilities of the genetic algorithm were used to optimize the relationship between discharge and sediment yields; then the results were used to calibrate and validate the SWAT model. The results indicate that genetics algorithm can be used for optimizing coefficient of sediment discharge equation and the result is better than sediment rating curve. Simulation of watershed hydrology using SWAT shows that the capability of the model in prediction of sediment yield and water flow is good. Using genetic algorithm to optimize the relationship between discharge and sediment has an important role in extracting daily sediment yield and simulation accuracy of the model. Also, the use of evolutionary algorithms can have a significant role in extracting the discharge -sediment relations, which usually is accompanied with a large error in experimental models such as a sediment rating curve.
Shirko Ebrahimi Mohammadi; Mahmood Azari; Esmaeel Manoochehri
Abstract
Introduction: Forest herbs due to decrease of runoff coefficient and the kinetic energy of raindrops, is known as a key factor in controlling runoff and soil conservation. Many physical (hydrophobicity, electrical conductivity, pH, particle size distribution, color and temperature regimes), chemical ...
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Introduction: Forest herbs due to decrease of runoff coefficient and the kinetic energy of raindrops, is known as a key factor in controlling runoff and soil conservation. Many physical (hydrophobicity, electrical conductivity, pH, particle size distribution, color and temperature regimes), chemical (quality and quantity of organic matter, nutrient availability) and biological (Microbial biomass, soil invertebrates living community) soil properties can be affected by forest fires. Fire not only reduces forest herbs, vulnerability against splashing rain but also has strong effects on the hydrological cycle and soil loss. despite of repeated fires, there are very few studies about fire impact on natural resources of the west of the country, especially the city of Marivan, in Kurdistan province so this study aimed to investigate the short-term fire impacts on soil properties, Hydrologic regime, soil erosion and sedimentation of Zrebar Lake watershed in west of Iran.
Materials and Methods: Considering the importance of the slope on the hydrological response of the watershed, slope classes of the Zrebar Lake watershed were mapped. Therefore, effects of fire on hydrological characteristics, erosion and sedimentation were studied by the establishment of twelve 0.25 square meter plots in three replications at two dominant slope classes (0 to 30 and 30 to 60%) in burned and natural areas . The first plots in the burned and natural sections, was established randomly and two other plots with the similar conditions at a distance of 1.5 meters from each other were established. Garden Spray Simulator with constant pressure was used to fall rain from half a meter height for thirty minutes with an intensity of about 2 mm min-1 and 1 mm droplet diameter according to the general weather conditions of the studied area. For every five minutes, runoff and sediment were collected. Runoff volume by weighting and suspended sediment concentration by drying at 105°c were measured. Infiltration and interception by water balance assessment and subtracting the simulated rainfall volume and runoff were calculated. Soil samples were also collected in triplicate by auger drilling method to assess the effects of fire on different characteristics of topsoil (depth of 5 cm) asthe samples 1 and 2 in the slope class of 30 to 60%, and samples 3 and 4 in slope class of 0 to 30%, at the burned and natural sections respectively. In the laboratory, after determination of soil texture, the moisture content, pH and EC by portable laboratory instruments, the percentage of total organic carbon and organic matter bye wet oxidation were measured. Soil water repellency by Water Drop Penetration Times (WDPT) method in the field was calculated. Statistical analysis for comparing the average hydrophobicity of the soil, runoff and sediment of both natural and burned treatments by independent t-test and for equality of variances by the Levene test was performed using SPSS 21 software.
Results and Discussion: The results showed no effect of fire on soil texture because the fire severity was low to moderate as the color of ash was black. The fire caused to 46 percent reduction of soil moisture and also 24 percent reduction of soil organic matter and 29 percent reduction of total organic carbon at 0% to 30% and 30% to 60% slope classes respectively. Slight increase in pH and electrical conductivity were another effects of fire. At the slope of less than 30%, the average water drop penetration time were 1.24 and 0.70 S in burned and natural treatments and at the slope of 30 to 60 % slope class were 4.52 and 1.04 S respectively. Independent t-test results showed that, the water repellency differences of natural (t=3.466, p=0.003) and burned (t=7.364, p=0.000) treatments were significant. Levene test and independent t-test results showed significant difference in the average of runoff at confidence level of 95% in both slope classes. At the slope of less than 30%, differences of sediment average of burned and natural plots with a significant level of 0.012 were significant. But in slope class of 30% to 60%, despite of large different sediment concentration output from the burned and natural plots at the beginning of the experiment, there was no significant difference between them. The results showed that fire leads to low soil moisture content, total organic carbon and soil organic matter. Slight increase of pH and EC and also lack of effect on soil texture, in both slope classes were also observed. Ash on the forest floor caused to soil water repellency and therefor decreased soil infiltration and increased runoff and soil erosion.
