مجله ترویج و توسعه آبخیزداری
پیاپی 12 (بهار 1395)

Snow coefficient is the ratio of annual snowfall to annual precipitation. Usually lack of snow data or impassable stations in mountainous areas, oblige us to use from empirical models. Therefore, evaluation the accuracy and calibration of the models for the region is essential. Chandra’s model calculates snow coefficient parameter using temperature data. In this study, snow coefficient to the measured data and Chandra’s model in a monthly and annual scale, for 11 synoptic stations in a five-year statistical period of (2007 to 2011) were compared using the mean square error and average accuracy deviation error. The Model was calculated the temperature range for snow from 1.2 to 2.5 at each station and the temperature coefficient for each station was determined by tested models. There is lowest coefficient in Shahrekord, bridge Zaman Khan and Dezzak stations (2.1) and highest in Oregon. The results showed that the model based of regional coefficient could estimate the annual snow coeffistationcient with more accuracy.

Climate change impacts on climate parameters such as rainfall, temperature, evapotranspiration and water resources. The aim of this research is the evaluation of the effect of climate change on climate parameters and evapotranspiration by the use of HADCM3 model in an arid (BandarAbbas) and semiarid station (ShahraKord). In order to simulate daily data of rainfall, sun shine, max temperature and min temperature based on a stochastic method, LARS-WG downscaling tool was used. This stochastic weather generator downscaled the climate of two synoptic stations by the use of HADCM3 model and A2, A1B, B2 emission scenarios during 2011-2030. The largest increase in the amount of max and min temperature was observed under A1B scenario in July in ShahreKord station. Winter precipitation increases in ShahreKord station base on all of the scenarios that it can be referred to the strengthening of the rainfall flows systems such as Mediterranean and Sudan Ian. Increased winter rainfall inBandarAbbas station can be attributed to the strengthening of the monsoon rain system. In both of stations, evapotranspiration increased in all of months and warm seasons. This increase is more considerable in warm months. Totally impact of climate change on rainfall behavior is different in both stations, while the other parameters of both stations have similar behavior.

Sediments are defined as loose particles of sand, clay, silt and other substances which are transported by water and finally deposited at the downstream of the watersheds water bodies. Sediments cover a wide range of diameters of transported particles. However, fine suspended sediments have been considered well due to their signifact relationship with transport of nutrients, tracers, heavy metals and other pollutants through river systems. Accordingly, undrestanding dominant processes of suspended sediment transportation in a watershed and authentic perception from the important related concepts such as sediment mobilization, sediment remobilization, sediment yield, sediment storage, sediment deposition, sediment redistribution, sediment budget and sediment cascades lead to handle problems of sediment associated pollutions and sediment management programmes. To this end, the present article tried to achieve the same appropriate undrestanding of aforesaid concepts and their processes importance and recall the importanc of holistic simulation of watersheds behavior in context of sediment management.

Due to importance of Harazriver in supplying drinking water, pollution of agricultural water around this river and also discharging several pollutants into it, water qualitative evaluation of this river seems necessary. The purpose of this research is zoning of water quality of Harazriver using NSFWQI index. In order to recognize the effect of agricultural and industrial wastewater and residential centers, investigated the qualitative parameters of river water in a 6 months period from February 2013 to July 2014 at interface discharge from Lar dam to entry of water into the Caspian sea in 6 stations. The results showed that the amount of coliform faecal, Do, temperature, nitrate and phosphate had significant variations in the entrance of river to the flood land, so that in Sorkhrood station in all months had significant different. The water of Haraz river in 5 stations (Poloor to Karesang), had medium class of quality with index of 50-70 in most months. Whereas in Sorkhrood station, had low water quality during all months. Also, the results of statistical analysis of T-TEST on discharge rates, temperature, TDS and DO parameters showed that two periods of low and high water had significant differences.

Different methods of measuring runoff and erosion may lead to different results, which are not necessarily related to specific effects of studied variable on erosion. Although runoff, erosion and sediment studies on the prepared soil in the experimental plots is inevitable because of many advantages, but the disturbance and transport of soil and prepared experimental plots reduces the reliability of these studies. All methods of preparing soils for use in laboratory experiments have one basic objective, namely, that the prepared soil sample should be as homogeneous as possible. Changes in soil during collecting, transport and preparation procedures including air drying, sieving and especially the effects of soil moisture during this process and finally, increasing the bulk density of the soil surface may affect the results of the runoff and erosion. A case study was therefore conducted to compare the surface runoff, sediment concentration and soil loss from the field plots with disturbed soil (prepared for experimental erosion plots) and undisturbed (natural soil). The results showed that the effect of soil disturbance on all variables including time to runoff, runoff volume and coefficient, sediment concentration and soil loss was significant (p≤0.01). Time to runoff, runoff volume and coefficient, sediment concentration and soil loss increased by 2.29, 3.45, 2.79, 2.83 and 11.50 times respectively after soil disturbance.

The current consumption trend of watershed resources causes the land degradation.Degradation in the long term is a serious threat for people who live in the watershed. Supplying the basic needs and in the same time securing the living environment for watershed dwellers are to be considered by the decision makers. This objective can be achieved by a comprehensive plan called "integrated watershed management". Identifying the watershed physical characteristics and defining its capabilities/limitations are the first steps of this plan. The previous studies performed in Fars Province were evaluated in order to identify the characteristics and limitations as well as grouping similar watersheds. The results showed that the Fars Province span is divided to 14 major watersheds at the basis of the two criteria "surface drainage" and "topographic conditions". These watersheds can be categorized to 5 environmental groups which are subjected to 27 threatening limitations. The main threats are environmental pollution, drought, floods, water erosion, desertification, salinity lands and surface water pollution. These limitations must necessarily be taken into account for the decision making and in the development projects.