سید سجاد مهدی زاده محلی

The source of many qualitative and quantitative problems of water resources is the activities that are done in a watershed. Therefore, reviewing the planning strategies of watershed can lead to the reduction of these challenges therefore it is necessary to assess the effects of operating of these strategies before implementing them.

This research is carried out in the Hashtgerd basin is located in the central part of Alborz province. After making the semi distributed hydrological model (SWAT), this model has been developed to convert quantity and quality of surface water resources. For this purpose, the statistics of hydrometric stations Fashand, Dehsomeh and Najmabad and qualitative data of nitrate of the index station were calibrated and validated as control points. After model sensitivity analysis, its calibration process was conducted using SWAT-CUP software with SUFI2 algorithm and 500 iteration and the best values of selected parameters were obtained. Then, impact of implementing management scenarios are required such as modifying cropping pattern and improving irrigation methods to enhance the agricultural efficiency for improving agricultural state and reducing the contaminations. At last assessing the vulnerability of the Hastgerd aquifer using seven DRASTIC parameters by overlaying layers, ranking and weighing was assessed.

The results of the monthly surface runoff simulation were tested by Nash-Sutcliffe indicators and coefficient of determination. The results above 0.7 which showed that the simulation was done with good precision showed that simulation was done with proper precision(results over 0.7). The results of the Nitrate calibration and validation show that the NS was 0.83 and 0.7 and the R2 was estimated .87 and 0.89. These values indicate the proper performance of the model and approve high correlation between the observed and simulated data. After determining the vulnerability map of the Hashtgerd aquifer along the density of wells correcting the weights of the model layers, the central part of the plain is the most vulnerable.

Two management scenarios were modeled including the change in the cropping pattern and improvement of the irrigation efficiency to assess the quality and quantity variation in surface resource. It was indicated, by modifying the cropping pattern and reducing water exploitation, the amount of surface runoff was increased. However, the density of Nitrate was reduced by 5 to 20 percent in different months. With implementation of scenarios, the water consumption in the agriculture sector will be reduced from the 85.3 MCM to 59.8 MCM. The final vulnerability index of the aquifer varied between 44 to 90 by using DRASTIC method.

Understanding the problem of seawater intrusion (SWI) in coastal aquifers plays an essential role in managing groundwater resources in these areas. This research examines seawater recession (SWR) in coastal aquifer in a laboratory scale; considering both homogeneous and heterogeneous environments, with and without a cutoff wall, and in a steady-state condition. For this purpose, different scenarios are defined in the laboratory, and all the effective parameters in the problem are considered and dimensionalized to facilitate salinity analysis. The laboratory data were analyzed using image processing technique and isolines with the concentration of 5%, 95%, and transition zone (Seawater hydrodynamic dispersion zone) were determined. The results showed that in a heterogeneous case, the rate of SWI was higher, and the efficiency of cutoff wall performance was higher in the homogenous case than the heterogeneous case. According to the present study results, the maximum effectiveness of cutoff wall in SWR percentage was obtained in 100% homogeneous and 92% for the heterogeneous case. The best location of the cutoff wall in this study with tank dimensions of 1 and 0.6 meters obtained 0.8 m from the tank bed and 0.2 m from the saline boundary. The achieved graphs helped to design the cutoff wall in actual media optimally.

The Khanmirza plain is one of Iran’s fertile plains that is located in Chaharmahal Bakhtiari province. Agriculture in the area is very prosperous, but the lack of rain and over-harvesting from consumption wells has led to a reduction in groundwater levels, even causing land subsidence. Moreover, the high usage of chemical manures, especially nitrate manures, has increased the number of solutes and chemical materials in the groundwater. Thus, for this plain, making artificial ponds is important to modify the storage of the aquifer. In this study, to define the optimum locations of the artificial ponds, the effect of 12 factors was considered. The analytic hierarchy process (AHP) method was used to introduce the weight of each parameter in comparison to other factors. Afterward, the spatial priority of all factors was derived using the Geographic Information System (GIS) technique. The produced GIS layers were laid on each other and the optimum locations were obtained. Agricultural drainage was an effective index for recharge purposes. The results of the study demonstrated that groundwater level decline got the maximum weight (40%), while the land slope had the minimum weight, since the vicinity to available floodways was considered as an independent criterion. The results also showed that regions with a total area of 18 km2 in north and north-west of the Khanmirza plain could be the optimum and most suitable places for artificial ponds construction.

In sedimentary rivers, mining of materials regardless of their location, can lead to rapid river displacement, destruction of river banks, arable lands, water structures and consequently makes social and economic problems. The main aim of this study is to recognize and evaluate all the effective parameters in material mining and determination of optimal site selection. In this study, the effective parameters that influence the extraction of river materials in Talvar River of Kurdistan Province have been evaluated using indexes as environmental, geological, geotechnical, hydrologic characteristics, social and economic conditions. For this purpose, Analytical Hierarchy Process (AHP) and Geographic Information System (GIS) are used. The priority of input indexes into the model is obtained using questionnaires from experts related to water and river engineering. The weighting of the parameters is performed afterward using AHP method binary comparison. The GIS technique is then applied to integrate the information layers by overlaying them. Eventually, the maps of optimum and suitable points were extracted for river mining. The morphological results of this study showed that the straight lengths of the river are more sensitive to the variations of bed level compared to meander sections and it is necessary to extract the material in these lengths with same depth and width. According to the results, sediment hydraulic index has the maximum weight due to determination of sediment deposit sites. The results also demonstrated that the first priority of river materials mining came to places that have low longitudinal slopes, placed in bends and are close to access roads.

Excessive exploration of groundwater causes seawater intrusion (SWI) in coastal aquifers. The purpose of this study is to investigate the effect of aquifer bed slope on SWI characteristics including salt wedge toe position, thickness of mixing zone and seawater volume in the aquifer. Different scenarios under various bed slope values and directions are defined and numerical dispersive SEAWAT code is used for modeling. Two different boundary conditions (i.e. constant head and constant flux) are also applied to freshwater inflow at landside. The simulation results demonstrate that in the confined aquifers with landside constant flux, the SWI extent and thickness of mixing zone have increased when the slope changes from a positive value (i.e. longitudinal slope toward the sea) to negative amount (i.e. longitudinal slope toward the land). The results of this study show that when the aquifer bed is considered flat, the SWI specifications including salt wedge toe position, mixing zone thickness at bed and saline water volume are less estimated than those in cases with negative slope and are more predicted than positive slope cases. Type of freshwater inflow at landside boundary also influences the results. In confined aquifers, when landward boundary condition is changed from constant flux to constant head, salt wedge characteristics were not significantly changed. Variation in the aquifer bed slope will affect the gravity factor (potential head) in the related equations that is accompanied with pressure head, which plays a key role on SWI specifications in confined coastal aquifers.

Population growth and scarcity of coastal freshwater resources have increased the stresses on many coastal aquifers, leading to aquifer storage decline and salwater intrusion (SWI). Investigation of coastal aquifers routinely involves the application of SWI models, which can be divided into two categories, namely sharp-interface and dispersive-interface approaches. There is no mixing between freshwater and saltwater at sharp-interface approaches. This makes them computationally more efficient while dispersive-modeling approaches are more numerically challenging, but allow for freshwater-saltwater mixing. Most coastal aquifers comprise overlying sequences of geological strata, resulting in SWI characteristics that may differ significantly to those of homogeneous cases. The layered coastal aquifers have received significantly less attention than the more simplified single-layer case, despite the fact that stratified aquifers are widespread. In this study, a sharp-interface approach (named as SHI-SWIM) was developed using FORTRAN programming code. The model is first validated and then applied for the simulation of sand-tank experiment and field-scale multi-layered aquifers exposed to pumping in order to evaluate the strength and limitation of the developed model. SHI-SWIM model produced better result for higher pumping rates. Additionally, the results of fully penetrating wells and closer position of well to shoreline matched better with the dispersive modeling outputs. In real cases, where the saltwater may wend a long distance toward the well screen, the sharp-interface modeling weakly matched with the dispersive modeling, specially in terms of well salinities.

Steady and unsteady experimental and numerical simulations are carried out in this paper to investigate saltwater intrusion mechanism into unconfined coastal aquifer. Laboratory results are compared to dispersive SEAWAT model to assess the applicability of numerical simulation. The dispersive SEAWAT model predicts salinities reasonably well comparing with sand-tank observation but it over predicts salt wedge toe position. Time reaching to steady state was almost equal in both physical and numerical modeling. In order to compare the mixing zone thickness, 5% and 95% salinity contours were also compared against laboratory data. The numerical results indicated partially wide mixing zone that is not observed in the experiments. Longitudinal dispersivity has been calibrated in the model to minimize the mixing zone thickness. Flow velocity components are also computed in this study by simple Darcy’s law and the freshwater and saltwater streamlines are depicted to visualize the flow adjacent the salt wedge and to observe the freshwater/saltwater movement toward exit point.

In this paper, spinning rate of sediment particle during saltation in turbulent flow was measured by means of high speed photography technique. Experiments have been carried out for different hydraulic conditions, particle sizes and densities. Particle spin was measured in five stage of saltation step by analyzing and processing picture taken at 250 frame per seconds. The results showed that increasing turbulence parameter of flow will cause increase in angular velocity and under the same flow condition, particles with larger sizes and specific gravities spin more rapidly.

This paper studies the mechanical characteristics of saltation of bed-load particles in turbulent flows. Experiments have been carried out by means of high speed photography to obtain saltation characteristics such as length, height, velocity, impacting and rebounding angles for different hydraulic conditions, particle size, density and bed roughness by analyzing and processing pictures taken at 250 frames per second. The measured values of the parameters showed that increases in turbulence parameters of the flow increase saltation length, height, and velocity but decrease the impacting and rebounding angles. It was also found that saltation length and height tended to increase as the average size of the bed material (d50) increased. To solve numerical trajectory equations, the initial velocity component of the particle must be known. The initial longitudinal particle velocity was found to range from 3u* to 8u* and its vertical velocity ranged from 1.5u* to 3.5u*, which were different from the values reported in the literature. The longitudinal and vertical components of the restitution coefficient were also measured and it was seen that the Shields parameter (*) had no meaningful effect on these components, remaining almost constant with increasing.