Irrigation
Hajar Norozzadeh; Mahsa Hasanpour Kashani; Ali Rasoulzadeh
Abstract
Climatic changes and human activities are among the important factors that affect the flow of rivers and it is very important to determine the contribution of these factors in order to better manage water resources. In recent years, there have been major changes in the watersheds, and the amount of runoff ...
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Climatic changes and human activities are among the important factors that affect the flow of rivers and it is very important to determine the contribution of these factors in order to better manage water resources. In recent years, there have been major changes in the watersheds, and the amount of runoff and river flow has decreased, or in some cases, the flow has increased due to the occurrence of floods. The issue of reducing the amount of runoff, especially in the arid and semi-arid regions of Iran, is one of the basic challenges related to the management of water resources. Hydrological changes primarily result from a combination of natural or climatic factors, including precipitation levels, air temperature, and overall warming of the Earth. Additionally, human activities, such as the construction of dams, creation of reservoirs, urbanization expansion, and indiscriminate harvesting, play a significant role. It is important to note that these factors are interconnected, and alterations in one can impact the others. The increase of greenhouse gases and climate change has caused a change in the hydrological cycle and the amount of runoff in the watersheds and has increased the number of climatic extreme events. The main purpose of this study is to determine the contribution of each of these factors on the discharge changes of the Gharehsoo River, one of the most important rivers of Ardabil province, using elasticity-based methods (non-parametric and Bodiko-based methods).
Materials and Methods
In this research, firstly, in order to determine the point of change in the amount of river runoff and to divide the base and change period, Petit's test was used during the statistical period of 1984-2019. This test was done using Xlstat software. According to the results of this test, there was a change in the annual flow time series in 1997, which was considered as the base period from 1984 to 1997 and from 1998 to 2019 as the period of changes. Then, the contribution of each of these factors was determined using elasticity-based methods.
Results and Discussion
In the elasticity-oriented method, the non-parametric method and the methods based on Bodiko's assumptions were used to calculate the elasticity coefficient.The results showed that in Samyan station, in the non-parametric method, the contribution of human activities is 88.26% and the contribution of climate change is 11.74%. The contribution of human activities and the contribution of climate change for the methods of Schreiber, Aldekap, Bodiko, Peek and Zhang, respectively 91.98 and 8.02, 90.02 and 9.97, 91.98 and 8.02, 90.80 and 9.20, 92.37 and 7.62 are estimated. In general, in the elasticity method, the contribution of human activities is 88.26 to 92.37 percent and the contribution of climate change is from 7.63 to 11.74 percent, depending on the non-parametric and Bodiko method. At the Dost-Beiglo station, employing the non-parametric method reveals that human activities account for 96.13% of the observed changes, while the remaining 3.87% is attributed to climate change. The contribution of human activities and the contribution of climate change for the methods of Schreiber, Eldekap, Bodiko, Pick and Zhang are 97.71 and 2.29, 97.42 and 2.58, 97.56 and 2.44, 97.48 and 2.52, 97.71 and 2.29 are estimated. In general, in the elasticity-oriented method, the contribution of human activities between 96.13 and 97.71 percent and the contribution of climate change from 2.29 to 3.87 percent, depending on the non-parametric and Boudico-oriented method, have been met.
Conclusion
In this research, different hydrometeorological data such as precipitation, evaporation and transpiration and monthly discharge from the Samyan and Dost Beiglo stations were used for the statistical period of 1982-2019. First, by using Pettitt's test, it was determined that the river flow rate has changed abruptly since 2016. Therefore, the entire statistical period was divided into two natural and change periods, and then, using elasticity-based methods, the contribution of human activities and the contribution of climate change were determined. According to the results obtained in both stations, the impact of human activities (more than 88%) on the basin's runoff is far more than climate change (less than 11%). Therefore, it seems necessary to prevent the effective human activities on reducing the river flow in solving and managing water problems in the basin.
Majid Homapoor Goorabjiri; Ali Rasoulzadeh
Abstract
Introduction: The forest residuals play an important role in runoff rate, soil erosion, and soil infiltration capacity of protecting mineral (surface) soils from the direct impact of raindrops. By intercepting rainfall, the forest residuals serve as a temporary reservoir and allows more time for infiltration ...
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Introduction: The forest residuals play an important role in runoff rate, soil erosion, and soil infiltration capacity of protecting mineral (surface) soils from the direct impact of raindrops. By intercepting rainfall, the forest residuals serve as a temporary reservoir and allows more time for infiltration into the mineral soil beneath (Kosugi et al., 2001). Hydraulic properties of forest residuals were unknown to some extent and could not be measured with similar methods used for mineral soil. In recent years, several studies on the forest floor have been published (Kosugi et al.,2001; Schaap et al.,1997). The objective of this study was the comparison of accuracy of van Genuchten and Brooks & Corey models for simulating water flow in forest floor using the HydroGeoSphere Code of broad-leaved, needle-leaved and mixed-stand floor. First, saturated hydraulic conductivity, porosity, and water retention curve parameters (van Genuchten equation) which were unknown parameters in the forest floor were estimated by inverse method. Second, estimated hydraulic properties were compared statistically.
Materials and methods: Forest floor samples were collected from broad-leaved (beech and others), needle-leaved (coniferous) and mixed-stand (coniferous and broad-leaved) trees in Guilan province, Iran. In the laboratory, a plastic wire-netting, composed of 0.3 mm diameter was attached to the bottom of each core sample to support forest floor. Then the samples were piled up to make long columns of 18.1 cm in inner diameter and about 40.88 cm in height. Artificial rainfall experiments were conducted on top of the columns and free drainage from the bottom of columns was measured in the laboratory. Applied rainfall intensities were randomly changed in the range of 0-0.01 cm/sec. Drainage at the bottom of the tray was collected and measured using an electronic balance. First, a constant intense rain was applied to reach to steady state condition as a constant discharge rate from the bottom was established in order to accurately define the initial condition required for the numerical simulation of unsaturated water flow. After reaching to state steady experiment, transient condition was carried out. In transient condition, the random rainfall experiment was conducted and the transient discharge rate from the bottom was continuously monitored. In this study, we developed an inverse method for estimating parameters based on the Levenberg-Marquardt (Marquardt 1963) minimization algorithm in the C++ programming language along with HydroGeoSphere (Therrien et al., 2008) as a forward model. The model was used to address two specific issues. First, it was used to estimate the hydraulic conductivity, porosity, and soil water retention curve parameters (van Genuchten and Brooks & Cory equations) which were unknown parameters in the unsaturated porous media. Second the water flow in the forest floor was simulated using van Genuchten and Brooks & Cory equations along with HydroGeoSphere code.
Results and discussion: The results of calibration periods showed that the estimated free drainage using the optimized parameters exhibits a good fitting with the observed free drainage for all treatments. The good agreement between simulated and observed free drainage in the validation period for all the forest floor samples illustrated that the estimated hydraulic properties efficiently characterized the unsaturated water flow in forest floor. So one could conclude that Richards' equation along with Brooks & Cory and van Genuchten's retention functions can successfully describe the unsaturated water flow in the forest floors.
Estimated hydraulic properties succeeded to reproduce the observed free drainage in the transient condition, indicating van Genuchten functions along with Richards' equation can be used to simulate water flow in the entire forest floors. The results of the study showed that the forest floor samples have large saturated hydraulic conductivity values like light soils. The results showed that inverse method was not sensitive to residual water content. Also the results showed that HydroGeoSphere code along with van Genuchten's retention function with 0.2753 mimics free drainage better than Brooks & Corey's retention function with 0.3400 but there is no significant difference (P
