مجله سامانه های سطوح آبگیر باران
سال سوم شماره 2 (پیاپی 7، تابستان 1394)

Deficiency of precipitation followed by water scarcity is one of the most important problems in arid and semi-arid regions. Among the water supply sources to these areas are collecting and storing rainwater. Site determination is finding a series of proper optional places for a particular applications that multi-criteria decision problem are involved. They are defined by simplified strategies for decisions and facilitate spatial process on various problems of spatial deciding in various ways. The aim of this study is to determine the potential sites of rainwater harvesting using Analytical Hierarchy Process in urban areas of Birjand. In this study, to obtain the proper area for rainwater collection from 5 criteria of slope, annual precipitation, land use, distance from surface canals and rivers in the study area were used. Initially to use this model, layers provided based on their relationship with the phenomenon are classified and scored. Then, they are introduced to the model. The final composition of the layers is configured of four classes, including the potentials of very high, high, medium and low categories. Results have shown that the criteria of land use, distance from river and surface channel take the largest weights of 0.584, 0.151 and 0.140, respectively. Finally, eleven points talented rainwater harvesting in urban areas of Birjand are identified.

Desertification control, especially using the floodwater spreading methods is a logical way that not only rehabilitation of groundwater reservoirs, but also improves some severely degraded lands because of suspended load in floods. In this essay, the descriptive-analytic method was used by library method and analyzing the results of the research projects. The results show changing the texture of the soil to the medium texture, decreasing of pH about 8 percent, increasing the organic matter about 6 times, increasing the vegetation that all of them have the significant effect on the reducing of the wind erosion due to floodwater spreading projects. Increasing of silt, clay and organic matter was caused increasing soil moisture therfore connected to the soil and stable against wind power, which reduces the corrosive force of the wind. So, flood water spreading will also play an important role in reducing of wind erosion in arid and semi-arid country without the tree planting. To search for a method to inhibit the effects of wind erosion, measure the amount of soil lost in the water spreading systems is recommended.

Nowadays, rainwater harvesting systems, especially in urban regions, are considered as one of the approaches in water resources management. It is globally being studied as an effective plan, as well. Therefore, considering the requirement of attention to the components of rainwater harvesting system and reservoir volume optimization, this study has been launched toward the optimization of required reservoir supply volume for enabling the maximum supply with the least expenses. In this work, the rainfall statistics of Birjand synoptic station was utilized as the base information for hydrologic analysis. To estimate water-consumption-rate, some questionnaires were distributed among residents. To determine an optimal volume for cisterns, simulated water harvesting systems were analyzed through mass curve analysis in two conditions, i.e. normal and wet years. Five scenarios were defined, in terms of water use rate in dry wet season. In the first scenario (the basic scenario without any reduction in water utilization rate in wet season), reservoir volume of the buildings 1-7 in normal year were estimated as 9794, 6099, 11021, 6282, 6196, 7026, and 17146 liters, respectively. However, in wet conditions (years), reservoir volume of the buildings 1-7 were estimated as 10104, 6931, 23013, 11774, 6488, 12501, and 36972 liters, respectively. For the scenarios 2-5, with 10, 20, 30, and 50%, respectively, decrease in residents’ water consumption rate in wet season, water was more supplied for dry season. However these scenarios resulted in some decrease or increase in reservoir volume. Obtained optimal reservoir volume of each scenario was compared with the basic scenario. Results have shown that the mass curve approach is appropriate for determining the volume of reservoir except for the buildings where the consumption curve was higher than input curve. In these cases, trial and error approach was identified more appropriate in reservoir volume estimation.

In undeveloped and less developed countries of arid zones, the easiest way for water supply is withdrawal of groundwater. The negative perception of this method of water discharge is clear. Floodwater Spreading is one of the water resources management strategies in arid and semi-arid zones that has positive impacts on groundwater resources. The aim of this research is to demonstrate the impact of floodwater spreading on quantity of groundwater in Hashtbandi Plain, minab, Hormozgan province, Iran. Annual changes of water level were determined by reviewing water level of monthly data (2003-2014) of five observation wells. Though the floodwater spreading may not stop the aquifer drop, it has reduced the drop intensity of groundwater level. Results show that the least drop is in observation wells 25 that is near floodwater spreading. The results have shown that before implementing the water spreading project, fluctuation of groundwater levels were proportional to the utilization of groundwater resources, showing a declining rate. After implementing the project, a turning point on groundwater level was observed. However, in the years 2011-2012 due to drought and lack of water filling utilization plan and increased ground water usage, water level has decreased sharply.

Human societies in arid and semi-arid have felt the necessity of rainwater for agriculture and even husbandry activities. Thus, they have used various methods for rain water harvesting. Todays, in most of countries in the world particularly those countries that are encountered the lack of water, using different methods of rainwater harvesting has been increased in most of countries. They are located in arid and semiarid regions wherein there is not enough rain. So water harvesting techniques are used even in humid and semi humid regions especially in summer season. In this approach we have applied one of traditional rain water harvesting methods in northern part of Iran for the purpose of providing the irrigation water for citruses garden in spring and summer seasons. It is called as isolated surface slope plate which was applied to a garden in GhaemShahr which is located in Mazandaran province. This garden is included an apartment with two stories. The first floor is belonged to settlement and in the ceiling floor is made water storage with 26 m3 capacity. Usually in every period of ten years the lack of water may occur. To solve this problem, the surface of the steep roof should be increased. On the other hand, if the surface of the garden increases, the surface of the steep roofs should be increased, too.

About 36 percent of the total rainfall occurring in the country can be harvested and more than 64 percent of it is evaporated. The annual rainfall in Iran is 432 billion cubic meters in which 280 billion cubic meter return to the atmosphere, while it can be used. The other 100 billion cubic meter by appropriate methods of water harvesting can be utilized. Although the rain rarely falls in the arid areas, its volume is considerable. The studied place in this research is green zone located in the beginning of Birjand-Qaen Road, with a length of 11 km, which is executed in order to the attractiveness of the city entrance and also the relative equilibrium of humidity in the area. The new and economic resources should be applied for trees irrigation due to the climatic characteristics and water shortage. Thus, the main goal of the research is the harvesting and collecting of rain water from the road surface, with a length of 9 km and directing it to the special tank and finally irrigating the green zone. The results show that due to the monthly shortage of water and water waste in the flow path, there is a capacity of storing 10000 cubic meter water in two tanks. This amount of water will be the supplier of the water shortage in the green zone. Also for optimal use and increasing the efficiency of irrigation, a drip irrigation system was designed for irrigation of the green zone.

Flood spreading in mountainous regions is very different as compared with plains. Flood spreading in Koohdasht, Roomeshkan and keshmahour plains includs gabion structures, stilling basins, diversion dikes, banquets, and channels. An average of 25 million cubic meters per year infiltrate into the plain. Planting 170000 tree species results in an increase in forage production and a reduction in flood damage. Statistics indicate that the plain Roomeshkan has not been faced with reduced groundwater levels and discharge rates of the wells are normal.