مجله علوم و مهندسی آبخیزداری ایران
پیاپی 9 (زمستان 1388)

Development of soil and water resources through flood spreading systems is one of the accepted methods in water resources engineering and management. At the time being, 35 flood spreading stations constructed in Iran, and covers about thousands villages and a million hectares of the flood area. Expenditure of the operation and maintenance of such a modern systems is a main constraint for the governmental management. Hence, dissemination of this modern system is restricted among local communities. Evaluation of these systems is the main objective of this explanatory research in Kashmar flood spreading station. The necessary data and information were collected and achieved by reviewing the secondary data, field survey and conducting workshops through Participatory Rural Appraisal (PRA), Rapid Appraisal (RA) and Participatory Diagnoses (PD). The results of this research showed that within 8 years of operation of this system, only 5% of the project area were covered by flood and the rest of spreading area remained unused. Therefore, as an economic aspect, it can be said, although the B/C is more than 1.14, the construction of such a huge system is not accepted. The benefit of groundwater recharges (more than 5 billion Rials over 8 years period) is too high in comparison to others outputs (lese than 0.4 billion Rials). These results show if we focus on limited objective (groundwater recharges only), it could be a solution for reduction of mentioned constraints.

One of the main targets of dam construction is to satisfy downstream water requirements in a watershed. Nutrients emerged from point and non- point sources deteriorate the water quality of the reservoir due to the eutrophication phenomena. In order to reduce the watershed nutrient load, Best Management Practices (BMPs) can be used to allocate the Total Maximum Daily Load (TMDL) which maintains the water quality at the standard level. In this paper, the Soil and Water Assessment Tools (SWAT) model is applied to evaluate the impact of BMPs on phosphorous load reduction at the watershed level.The methodology is developed to reduce the eutrophication of Satarkhan reservoir in Aharchai river watershed and supply the downstream demand with least cost of BMP implementation. In order to assess the impact of BMPs, different scenarios are defined including point source reduction like wastewater treatment and non-point source control including detention pond, grassed waterway and filter buffer strip. In each scenario, total phosphorous load input to the reservoir is estimated and its impact on the reservoir phosphorous concentration is simulated using the Chapra’s model. The hedging rule model for reservoir operation is used to evaluate the downstream demands considering the inflow to the reservoir. The developed scenarios are ranked based on the execution cost, reliability of water supply and the phosphorous concentration in the reservoir as the eutrophication index.

The permanent measurement of discharge even in general conditions is difficult and very expensive and the related problem is increased when floods take place. Towards solving the problem, it is tried to develop discharge-stage relationship through reading the stage and measuring the associated discharge in particular conditions. In this study, the stage-discharge relationship was developed and then analyzed for different time scales of rising and falling limbs of hydrographs, daily, monthly and seasonal by using bivariate regression and classic discharge rating models. The study was conducted in Kojour Forest Educational Watershed with an area of 13253 ha in Mazandaran Province, Iran. The results showed that the developed relationships, for each time scale, are specific, so that they cannot be applied for the other scales with reliable accuracy. The linear and power regression models with the minimum correlation coefficient of 58%, the maximum respective calibration and verification relative errors of 70 and 75%, lower RMSE and the minimum efficiency coefficient of 35% were also found superior to and more accurate than classics models for all study time scales.

This research studies empirical equation for abrasion of stilling basin caused by impact of the sediment. Review of previous papers shows that in previous researches, the mixture effect of erosion and impact are studied without determination of the share of impact in the mixture effect. Also in the researches, the sediment grain size is not as large as debris size in debris flow or experiments are done without tail water depth. Therefore, in this research, the impact of large grain size is studied on concrete stilling basin with tail water. First dimensional analysis is carried out, and subsequently experimental plan is designed. The experiment includes concrete samples with three different cement contents, five depth of tail water, three grain sizes. Abrasion of each grain impact is measured and recorded. Uni-variable and multivariable regression analysis was employed to find possible relation between abrasion ratio and the dimensionless parameter of the experiment. The empirical equations are judged using mean absolute relative errors of the equations. Then a multivariable power equation is proposed for determination of the impacts of abrasion of sediment. The equation shows the abrasion is function of dimensionless energy of sediment grain and the ratio of the grain velocity on stilling basin to the grain velocity on water surface.

Due to difficulties in measurements of snow characteristics in mountainous areas, use of IRS satellite images and extracting information of snow cover in watershed is a common practice. These information can be utilized by statistical models such as bivariable and multivariable regression models to estimate the snow- melting runoff.This research was carried out in Zarinerood (Bokan Dam) watershed in West Azarbayijan Province due to its importance in water resources supply.In this research, in addition to remote sensing data, the data from climatology, snow and hydrological stations are used to present regression models to estimate river runoffs.The results from multivariable regression models with two criteria such as R² and DV (Difference in Volume) for December, January and February of 2006- 2007 in Zarinerood watershed are equal to 0.94, -13. 48, respectively. The bivariable model for R² and DV presented 0.81 and -19.36, respectively. For calibration of statistical models, the level of snow covered areas are measured by IRS satellite images. The results presented based on RMSE, RE and QE cretia. RMSE for bivariable and multivariable regression models is 0.2 and 0.01, respectively.

The effects of climate change and a change on snowmelt runoff timing is very important in the rivers with snowmelt runoff regime. In this study the snowmelt runoff model (SRM model) and world climate change model (ECHAM4 model) are applied in order to study the effects of climate change on snowmelt runoff timing with two scenarios (A & B) for next 50 years (2000- 2050) in karoon basin in the southwest of Iran. Research results show that a shift is observed in peak time on snowmelt runoff from spring to winter and the winter stream flow is going up (10%) and the spring stream flow is going down. The summer stream flow is going down slightly and the autumn stream flow will not change considerably.

Snow as one of the precipitation forms has important effect in hydrological cycle and water resources management. Snow monitoring particularly in mountainous basin without modern technology is very difficult, according to temporal and spatial variation of snow property. Remote sensing is one of advanced technology in measurement of snow properties. MODIS imagery is one of new sensors that provide the possibility of snow cover measurement. In this research, we investigate ability of MODIS imagery for detection of snow cover from other phenomena such as cloud and earth using. Some methods of snow cover detection have applied in Haraz basin that is one of important basin in North of Iran. Results showed that false color image of moderate infrared bands has ability of snow and cloud detection and the best algorithm is the one that can envisage digital number of pixels deviation.

Land use changes and the development of road network and residential areas have caused an increase in runoff generation and flood hazard. The present study has been done to investigate the effects of land use changes on runoff generation and flood hazard in Kasilian watershed. The study of land use changes has been carried out by using aerial photos, topographic maps with scale of 1:25000, land use maps and satellite images. Also a rainfall- runoff model has been presented by using GIS (HEC- GeoHMS extension) and hydrologic model (HEC-HMS). We used the SCS and CN methods (hydrograph simulation and runoff height estimation) for presenting the hydrologic model. It is noted that the optimized model is validated by the other four events of flood. Then, land use changes have been included in the validated hydrologic model and their effects on intensifying runoff generation and flood hazard have been investigated quantitatively. The results showed that land use changes caused an increase in runoff generation potential and flood hazard.