Journal of Hydrosciences and Environment
Volume:3 Issue: 6, Dec 2019

In this research, an MLP neural network, which has widely been used in geotechnical engineering problems, is selected and trained by defining the stability factor of an earth dam. To training the network, we first specify the effect of parameters on the earth dam stability, including dam height (H), dam width (B), dam slope (θ), internal friction angle (φ), specific gravity of soil (γ) and cohesion of soil (C) by the Plaxis finite element program. Then, a database of 240 earth dam models is created and used to train the network. Subsequently, we train a single-layer and a two-layer MLP neural network with LM method and compare them. The results show that the single-layer network exhibits better performance in processing time and training quality. Then, the results are compared with the results of the ANFIS network and it is shown that the ANFIS network has a lower capability in defining earth dam stability factor than the MLP network.

This study experimentally investigated the effect of surface roughness of cylindrical weirs and upstream sedimentation on discharge coefficient (Cdw), pressure distribution, and energy loss under free and submerged overflow conditions. The tests were carried out for a non-sedimentation upstream channel bed and sedimentation levels of 2/3 of the weir height (P). Three different weir diameters and four degrees of weir surface roughness were used with a broad range of flow discharge. The comparison of Cdw of weirs indicated that Cdw can be reduced by 8 percent with the increase in the surface roughness from almost 0 to 4.5 mm height. Moreover, Cdw was increased up to 4 percent with the increase in the upstream sedimentation level to 2/3P. In addition, Cdw was reduced by 3-7 percent with the increase in roughness to 4.5 mm at the upstream sedimentation level of 2/3P. Cdw was also increased up to 5 percent and the energy loss was decreased to 15 percent as the weir diameter was increased from 0.15 to 0.25 m. It was found that, in all the studied weirs, the energy loss was increased up to 14 percent with the increase in surface roughness, whereas it was reduced by approximately 22 percent with the increase in the upstream sedimentation level to 2/3P. The comparison of the results showed that the pressure variation along the weir at the sedimentation level of 2/3P followed a similar trend to that obtained under non-sedimentation level conditions. However, the magnitude of pressure was reduced with the increase in the upstream sedimentation level. In addition, the effect of roughness on the pressure distribution over the weirs was greater at the downstream face than at the upstream face.

Given the recent droughts, it has become increasingly valuable to plan for water resources management and conservation as well as the protection of local communities. Investigating the trend of water resource changes, especially those that are restricted and have undergone transformations over a short period of time, is applicable for optimal resource management. The present study aims to evaluate physical changes in Fars province's aquatic zones, i.e. Bakhtegan, Tashk, Maharloo, and Parishan lakes, using the MODIS (Moderate Resolution Imaging Spectroradiometer) service and its relationship with precipitation over the period 2001-2017. Due to land-use and precipitation changes, the areas of these aquatic zones have decreased dramatically. As the results show, the area of the province's water surface along with the wetland class was 1346.31 km2 in 2001, comprising 1.09% of the total land use of the province, while the amount of water in the province (wetland and aquatic land-use classes) was 99.59 km2 (about 0.75%) in 2017. This indicates a decline of more than 25%. Then, using precipitation data, the relationship between the area of aquatic zones and the precipitation rate was measured. The results indicated a direct and positive correlation between these two factors as 0.76. The highest precipitation concentration was observed in the studied aquatic zones. The reverse was also true in the years when the lakes reached their minimum areas.

Water is a necessary but scarce input among the inputs used for crop production, so determining its economic value can be a good instrument to improve its management. In this respect, the present study aims to determine the economic value of irrigation water under drought conditions and to propose a cropping pattern and estimate farmer gross margin in the Qazvin plain in Iran using linear programming and positive mathematical programming (PMP) models. The statistical data were of the document type for the 2013-2014 growing season. The results showed that the economic value of irrigation water is 1,161 IRR/m3 whereas farmers pay 417 IRR/m3 as the water price. Also, the economic value of irrigation water is 1,152 IRR/m3 in the base year, which increases by 12.2-94.1 percent to 1293-2236 IRR/m3 under the scenarios of water limitation by 10-50 percent. In these conditions, farmers tend to reduce the acreage of sugar beet and sunflower and increase the acreage of irrigated wheat and barley. This will reduce farmers’ gross margin. This reduction of gross return is maximized when the costs of coping with drought and production costs are maximal. So, timely informing of farmers before the occurrence of drought and holding training courses about methods to counteract the negative consequences of this climatic phenomenon by governmental agencies, such as Jihad-e Agriculture Organization and research and educational centers, can be helpful in supporting farmers and officials in their attempts to cope with the consequences of drought. Determining the economic value of irrigation water across the region and accepting a reasonable price as water price by farmers can lead to a considerable saving of this scarce input in the region. So, it is recommended to price irrigation water in accordance with its economic value and the consideration of its equivalence.

This study characterizes land subsidence in Feyzabad plain, central Iran, using Sentinel-1A SAR data. These techniques are based on the analysis of pairs of synthetic aperture radar (SAR) images that are able to identify sub-centimeter changes in the line of sight (LOS) position of targets. Excessive groundwater withdrawal has caused several land subsidence in the studied area in the past few years. Using remote sensing techniques and SAR data, we analyzed the rate of land subsidence and its associated landforms in the area in a short time span. Feyzabad plain is located in an arid region with 154 mm annual precipitation. The most famous fault in the region is the Darouneh left-lateral fault with an east-west trend. To investigate land subsidence and the related effects, we first monitored ground motions between 2017 and 2018 in a 45-day period (for each pair of images) using SAR data and SNAP software. Then, we extracted linear landforms for each year to analyze subsidence in more details. We also mapped NDVI for both years so that we could compare the displacement and the vegetation cover in the studied area. Results showed that the maximum rate of subsidence was 3.9 cm in 2017 while the maximum rate in 2018 was 1.3 cm. NDVI maps revealed that decreasing pistachio cultivation has direct effects on the rate and magnitude of land subsidence. Results also showed that intensive subsides were centered in 2018 while in 2017, subsidence was scattered across the region.

Groundwater has often been considered one of the major sources of drinking and agricultural water, particularly in arid and semiarid regions. In this respect, the present study dealt with a combination of numerical models of groundwater and water resource management model. The first conceptual model was prepared to simulate the groundwater table of Birjand plain in South Khorasan province, Iran. Then, the groundwater level was predicted and verified using numerical models. The output of these models was used to investigate the influence of parameters such as climate change and population growth rate on the groundwater level within the WEAP management model. The scenarios discussed in this research included the assessment of the demand rate and saving underground water resources by increasing the rate of population growth, reducing the planting area, and using drip irrigation method instead of traditional irrigation practices until the year 2020. The results showed that by reducing the planting area to 20% by the year 2020 and using drip irrigation with an efficiency of 90% instead of traditional irrigation would reduce water demand by 14% and as a result, an average rate of 8.2 million m3 of water would be saved from 2016 to 2020.