مجله سامانه های سطوح آبگیر باران
سال پنجم شماره 4 (پیاپی 17، زمستان 1396)

Various methods have been used for collecting water, but each one by itself has shortcomings that have prevented or limited its application. The method of rainwater collection by using a rainwater harvesting device (rainwater harvesting machine or R.H.M) is a new technique that was inspired by pitcher irrigation, techniques of water harvesting, and drip irrigation. Combination of these three methods had led to the manufacturing of a very simple and practical device that can be used in various parts of the world (including Iran), especially in arid and semi-arid and even in semi-humid regions where access to water is limited or impossible. This device has applications in supplying the water required for agriculture, drinking, tourism, etc. Rainwater harvesting devices have completely overcome the disadvantages of the three methods mentioned above. It is a simple and multi-purpose tool, and its main application is to provide sufficient water for establishing and developing orchards, planting trees in regions where water is scarce or unavailable, and job creation. Protection of groundwater resources and prevention of erosion are among the most important additional goals in utilizing this device. In the present research, two samples of rainwater harvesting devices with the capacities of storing 430 and 1800 liters of rainwater were first designed, produced, and installed. A rain gauge was then used to measure daily rain and the volume of rainwater stored in the tanks of the devices, and to study their ability to store and save rainwater. Results showed that the devices had the necessary efficiency for harvesting and storing rainwater for when water was needed. The total water loss during the processes of rainwater entrapment and storage until the time it was used amounted to less than five percent.

Zayandeh-rud Basin is one of the most sensitive basins in Iran, politically, socially and economically. In the last two decades, the Zayandeh-rud basin has suffered from water stress, with about three-fifths of the length of the river in the middle and lower parts facing instability of water resources which have made those sections of the river seasonal. Due to the river water drying, water allocation to agricultural sector has been difficult, as water has flowed in the river only 5 times in the last decade, each time for few month. The closed condition and generative property of the Zayandeh-rud basin is such that the rate of exploitation of groundwater affects the occurrence or intensification of water instability in the basin. In this research, studied groundwater resources (Qanat, well) and springs in Zayandeh-rud basin are studied and compared during 2006 and 2011, two years in which a census was held. The results of the study show that after water resource instability, farmers tried to compensate for water reduction through well drilling and underground water utilization in order to continue their activities. This can be seen in the increase in the number of wells from the middle parts of the basin to the end of the river. In 10 years (2001-2011), about 9,000 wells were drilled to compensate for lack of water in the Zayandeh -rud basin and during this time, the average groundwater table level has fallen by an average of 5 meters. In addition, during this period, the qanats in Zayandeh-rud basin have either dried or showed reduced output. Similarly, the number of springs reduced due to climatic causes. Increased exploitation of underground aquifers has exacerbated the unstable condition of water and drought in the basin.

Estimating base flow rate and ground water recharge in a watershed is one of the most important issues in the management of water resources and hydrology. Since the river-aquifer system is a system with two inter-related elements, it is necessary to investigate base flow versus groundwater table of the aquifer to evaluate groundwater recharge estimation methods. In this study, PART and RORA software packages were used for base flow separation and groundwater recharge estimation based on the daily flow data for the Chenar Rahdar River. Also, the correlation between estimates of the two methods and groundwater levels was calculated. In this study, RORA was used to estimate the mean annual recharge during the statistical period using a recession curve displacement method which gave an estimate of 329 mm; using PART a discharge rate of 301 mm was estimated. RORA estimates the recharge rate above the discharge rate. The results of this study showed that there is an inverse relationship between estimates of the two methods with groundwater table. The average base flow index represents 65 percent of the overall flow at the station. Also statistical tests showed no significant differences between rates of groundwater discharge and recharge.

Climate change is one of the most important challenges which have affected various aspects of human life. In this study, first the type of climate was studied at the base period (1979-2009) at two stations of Urmia and Khoy. Climate was also identified according to the classifications of De Martonne and Selyaninov. After assessing the capability of the LARS-WG downscaling model during the base period, two models which were most similar to the base period of the studied regions were selected from general atmospheric circulation models for future studies. Assessing the effects of climate change on rainfall and temperature patterns at the two stations in the period from 2011 to 2040, De Martonne climate classification in the past period for the Urmia station and all scenarios of the two models of HADCM3 and HADGEM1 indicate a semi-arid climate. The results show that under the influence of changes at the Urmia station, the De Martonne drought factor will have an increasing trend and the region will shift from a semi-arid climate in the base period, towards a Mediterranean climate in the future period. According to the Selyaninov climate classification, this coefficient will increase in all scenarios of the two selected models, except for the A2 scenario of the HADGEM1 model. Regional climate will move from dry steppe to wet steppe. At Khoy Station in the base period and all scenarios of the two selected models of HADCM3 and ECHO-G, according to the climatic classification of De Martonne, the climate was dry and influenced by climate change. The De Martonne climate factor will decrease and the region becomes drier. According to the Selyaninov climate classification for all scenarios, the Selyaninov coefficient shows a downward trend. Thus, the climate of the region is desert type and due to increasing temperature and decreasing rainfall, the climate of the region will become drier and more arid in future periods.

Reduction in rainfall, population growth, environmental issues, and a need for development of green areas in residential buildings have become a major challenge for water resource management. The majority of urban surfaces are impermeable and as a result precipitation mostly flows on the surface as runoff. Hence, storage of rainfall in dry urban areas has an important role in water resource management. Tehran, with a population of more than 10 million people, has a dry semi-arid climate. Storage of rainfall can be effective in providing water for various purposes. The aim of this study was the evaluation of rainfall in Tehran and to assess the required volume of storage units to be built on roofs by designing and optimizing collection reservoirs for irrigation of green areas in residential units. To this end, precipitation data of two synoptic stations of Shemiran and Mehrabad, have been used for the northern and southern parts of Tehran, respectively. The evaluations were performed under two scenarios. In the first scenario, the highest monthly rainfall, and in the second scenario, the average annual precipitation was considered and storage volumes of tanks were calculated for roofs with areas ranging from 100 to 550 square meters. The results showed that in Tehran, using rainwater harvesting system in the months with the highest rainfall can meet the needs of green areas in drier month, as well as some other non-drinking water uses. Under the scenario which utilized the months with the highest rainfall, for every 100 m² of roof space, about 5000 liters of rainwater can be stored which lessens the pressure on the municipal water supply network and offers economic benefits .

Watershed management undoubtedly influences all water balance equation parameters. One of the most important parameters that influence runoff is land use change. Atashgah Basin, one of the most important sub-basins of Yadyboolikkchay, has an area of 40.50 km2 and is located to the east of Sabalan Mountain. In this study the effect of land use change on flood hydrographs was evaluated for the time period between 1968 and 2011. Land use map from 1968 was prepared using aerial photographs and land use map for 2011 was prepared using land use map of Ardabil province and the Google Earth package. To estimate maximum daily precipitation, data from 9 rain stations were used. Maximum daily precipitation data were prepared, completed and normalized. 8 probability distribution functions were evaluated using 3 statistical criteria. Maximum daily precipitation was calculated for 2, 5, 10, 25, 50 and100 years return periods using a log-normal probability distribution function. For simulation, the WMO rainfall pattern and the SCS rainfall-runoff model were selected. Results showed that dense rangeland areas had decreased and area of residential and agricultural land had increased, which have cause an increase in curve number during the 43-year period. Hydrograph simulation results for the two ends of the interval showed that maximum flood flow increased greatly with increase in return period, at low return periods (2 to 10 years). There was a small difference between 1968 and 2011 in terms of flood flow at mentioned return periods. Difference between flood flow of 1968 and 2011 increased with increas in return period (decreased permeability). Results, also showed that, land use change of Atashgah basin within 43 years decreased soil permeability and increase runoff.