مجله مهندسی و مدیریت آبخیز
سال ششم شماره 3 (پاییز 1393)

Soil Organic Matter (SOM) is one of the most vital components in soil solid phase and plays an important role in soil aggregation. SOM considerably improves soil physical conditions during long time. Moreover, knowing the SOM content of arid and semi-arid areas could significantly affect the soil management in such SOM-lacking regions. The objective of this research was to compare four common statistical models with the purpose of acheiving the best model for estimating the SOM in Ivanekey and test the obtained model in another semi-arid area of Urmia plain. Two Hyperion images were collected for Ivanekey and Urmia plain which were used to identify the relationship between spectral bands and SOM by applying SWR, MinR, PLSR and PCA models. Models were calibrated by Ivanekey Hyperion images and verified by nine Ivanekey and 23 Urmia random samples. Results indicated that MinR and PCA models do not have reasonable accuracy, but SWR and PLSR can provide the highest accuracy with the same RMSE value of 0.18, and R2 of 0.69 and 0.66, respectively. It is also demonstrated that there is a close relation between SOM and Red and Short Wave Infra Red spectral regions.

In order to reduce the losses caused by floods and economize flood control projects in an area, construction of appropriate structures and operating watershed practices in areas with high risk of flooding is essential. One of the approaches to identify high risk flooding regions is watershed simulation and evaluation of sub-watersheds participation in outlet discharge. In this research, hydrological units of Hamedan-Bahar basins were simulated using ArcGIS and HEC-HMS hydrological model. Then, flooding indexes were calculated and their changes in all sub-basins were mapped.Effective hydrological units on peak discharge were identified and prioritized for watershed management, by reviewing and comparing these indexes. Site selection of flooding indexes showed that Bahador Beyg and Qareh Aghaj sub-basins had the highest and the lowest effect on flood peak, respectively. Analyzing results demonstrated that sub-basins with large areas or with huge amount of runoff not necessarily cause more effect on flood peak. Performance of management practices and construction of suitable hydraulic structures in studied hydrological units efficiently reduce flood damages in Hamedan-Bahar basin.

Determination of environmental flow in river systems and other watery ecosystems is a new science in Iran and other developing countries. This paper evaluates the ecological requirement in a typical river by different hydrological and eco-hydrological methods. In this study, environmental requirement of Zarrinehrood river (located in North West of Iran), from downstream of Bukan dam up to Urmia lake (near to 140 km), was estimated by four Tennant, Tessman, Desktop Reserve Model (DRM) and FDC Shifting using the hydrometric data of Sariqamish station. According to results, the amounts generated from FDC Shifting method are more proper because of considering the ecological management qualification. Therefore, 16.7 CMS (equals to 33% of mean annually flow) was obtained as average environmental requirement of Zarrinehrood river in ecological management class C (maintains minimum ecological term in river). Also, monthly distribution of recommended environmental flow was compared with monthly flow of Sariqamish hydrometry station. The critical period for the river is during August to October. In this period, the monthly flow of 12.6, 11.6 and 6.3 m3s-1, are required to flow downstream in order to preserve the river life.

Soil erosion is one of the most obvious factors of soil degradation. Vegetation can affect on maintaining soil fertility and the amount of soil loss by reducing runoff and sediment. This study was conducted in Maraveh-Tapeh in the north-eastern part of Kalaleh watershed, located in 55◦ 56' 35" and 37◦ 49' 01" to investigate the role of plant species on soil stability with in a randomized complete block design with five treatments and three replications. Crop and pasture plants as herbal treatments were included Medicago sativa, Agropyron elongatum, Cyminum cuminum, Hordeum vulgare and a mixture of alfalfa and Agropyron. Plots were considered to have a 22 m long on slope direction (10%) by a wide of 5 meters. Runoff and sediment collecting tanks were installed at the bottom end of each plot to measure runoff and sediment. In this study the effect of cultivated plant species on the amount of soil erosion and fertility was investigated. The average volume of runoff during four years of executing the project was 6.93 and 22.9 m³ha-1in treatments of Hordeum vulgare and Cuminum cyminum, respectively. The average amount of sediment yield was 48.42 and 124.72 kgha-1 in treatments of mixed Medicago sativa and Agropyron elongatum and Cyminum cuminum, respectively. Results also demonstrated that Cyminum cuminum is not an appropriate species for cultivation on steep terrains with the aim of soil conservation due to its reverse effects on increasing runoff and reducing soil fertility in Maraveh-Tapeh.

The Lake Urmia is the 20th largest lake and the second hyper saline lake in the world. In recent years, the drying out of the Urmia Lake has attracted attention of many researchers. The main motivation of this study is to evaluate the role of drought in this disaster. For this purpose, Standardized Precipitation Index (SPI) and Reconnaissance Drought Index (RDI) are employed. The data for analysis including precipitation and temperature was provided from two global databases: GPCC for precipitation and NCEP/NCAR for temperature. The study was performed at the time span of 1980-2010 and the results showed that the Lake Urmia basin has experienced a severely drought during 1999-2000. After this period and during eight subsequent years, the negative effects of this drought could not be reduced completely by near normal to wet condition of the basin. Moreover, another severely drought occurred at 2008. RDI value for the 1999 drought was found to be -2.23 which is related to the extremely dry condition. The value of SPI for the same region and same year was obtained as -2.13. This comparison for other severe and extreme cases shows that RDI is more sensitive than SPI at the tails of the phenomenon. It was also observed that after 2000, while the region, in terms of rainfall and drought conditions, is generally close to normal condition, the lake follows a continuous decreasing trend up to the present time. Therefore, one can conclude that in addition to drought, other factors contribute to the drying out of the lake. The results indicated that the anthropogenic effects are responsible to some percent in this disaster. Construction of reservoir dams for agricultural development and other activities for job creation purposes like constructing fish ponds has intensified this crisis. The span of these activities is concurrent to the periods which the drought indices show the fragile condition of the basin in terms of available water resources. This fact emphasizes the importance of drought monitoring as an inseparable part of an IWRM program to prevent a nationwide disaster.

The purpose of this study is to determine the contribution of each lithological units in sediment generation of watershed. In this study, samples were collected primarily from sediments of small dams and sediments of waterways. Grading was performed for all samples by wet sieving. Then, 600 micron and 4 mm sieves were selected as indicators and by choosing 100 grains of sediment from each sample, mineralogical analysis was performed using a binocular and considering mineral and rock fragments the results were compared and adapted with the lithological units and the share percentage of each stone, each mineral deposits were determined by counting the number of minerals and rock fragments. According to the results, Єz lithological unit has the highest share in erosion and sediment yield with a 44.62 percent. This unit consists of pink to red Micaceous shale. PMl lithological unit with 22.88 percent is in the second place consisting limestone. The third lithological unit that has the largest share in sediment yield is Ev unit, which consists of andesite and andesitic breccia with layers of tuff and tuffite. Pl-Qc, Єl, Qt, Js, Et, Ek1, Pd, Єbt and Ef units with 4.25, 3.22, 2.09, 2.05, 2.01, 1.83, 1.33, 1.32 and 1.23 percent are in the next order and have the highest share in the erosion and sediment yield of watershed.

A check dam is a small dam with a simple and low cost structure and because of its specific material and simple building technology, it has a wide range of applications in flood control projects. In this research, the effects of check dams on reducing the flood peak and increasing the time of flood flow to reach to peak were investigated for Kan basin in north-west of Tehran. The hydraulic and hydrologic situation of the Kan basin was modeled using HEC-HMS software. Using hydrologic modeling the effect of building check dams on flood characteristics was studied in three scenarios of river slope change. The results showed that check dams reduced the flood peak to reduce between 0 and 0.9% in the first scenario (0.5 of the natural slope) and from 0.4% to 3.5% and 3.9% to 10.6% in the second (0.1 of the natural slope) and third (0.01 of the natural slope) scenarios, respectively. The time to peak also increased from 10 to 50 minutes. In hydraulic-hydrologic modeling, the effect of constructing check dams with no sediment in their reservoir was investigated for rainfalls of different return periods. The results revealed that with increase in rainfall return period, the effect of check dams on reducing flood characteristics will decrease. For instance, in the case of 100 check dams, the percentage reduction in peak outflow will decrease from 22.8 to 1.2 % for rainfalls of 2 and 20 years return period, respectively. In general, construction of check dams has no considerable influence on reducing constructive effects of floods. In other words, check dams should be used together with other structural and non-structural flood control methods.

Scouring around the bridge piers is one of the most important issues in bridge piers hydraulic. This phenomenon has led to a discharge under the bridge piers and the results caused their reversal. The local scour mechanism around the piers is very complicated issue and many researchers were conducted to discuss the investigation of this important matter. Many bridges are destroyed due to their often piers scouring and causing human and financial losses. Generally, two fundamental factors of flow contact with the bridge pier and water flow separation from the pier, led to the formation of vortices around the pier at the bridge piers site and cause the local scour. The present research has investigated the effect of flow discharge and pier diameter in depth and scour volume around the bridge piers using a physical model. For analyzing the effect of flow discharge and also the size of the pier diameter on local scour around the bridge piers, three piers were used with 21, 30 and 40 mm diameter with five different discharges in each pier. Experiments were carried out in a sandy bed (with a median size of 0.88 mm) flume of 8.0, 0.255 and 0.3 m in length, width and height a, respectively. The results showed that by increasing the discharge and Froude number in each pier, the volume and scour depth were increased. In a constant Froude number, the volume and scour depth increased by increasing the pier diameter. In 21, 30 and 40 mm piers, the scour depth also increased by 128.5, 94.7 and 135.1 percent by increasing of 40, 68.7 and 23.9 percent of flow discharge.

The ogee spillway with an arc plan has a longer crest length. Therefore, in a specific reservoir water level, it can discharge higher flow rate compared to a straight one and due to this reason is preferred in applicable plans. The aim of this research was to laboratory investigation on the effect of the curvature of the ogee overflow weir on distribution of flow discharge, determination of discharge coefficient and study the overall hydraulic behavior. This research was executed on Germichai Dam spillway physical model which was constructed in the Soil Conservation and Water Management Research Institute hydraulic lab. Results showed the need of correction on initial design and that the discharge coefficient of this free overflow is nine percent in average, less than ogee spillways with straight axis On the other hand, the geometry of the downstream conveyance conduit forces the spillway to act in a submerged condition for discharges higher than 1.3 times the design discharge And the discharge coefficient presented a decreasing trend with the upstream weir head.

Launching satellites with Synthetic Aperture Radar (SAR) sensors onboard, purposely built for differential interferometry (D-InSAR) applications opened new opportunities for mapping and monitoring slow ground deformations and even high speed landslides, for the updating of regional landslide inventories as well as retrieving time series of landslide movements. The present work has been done by using DInSAR method, with objection of performance assessment of two radar sensors in order to detecting, monitoring and landslide inventory mapping in Dena Mountain of Zagros located in south of Isfahan province. For this purpose two sets of images including 17 and 21 RADAR images of PALSAR and ASAR sensors from ALOS and ENVISAT satellites were chosen and processed by D-InSAR method. The preliminary processing result showed that 16 interferometer images were suitable for the next processing stages from all applied data sets. The outcome of interfrogram analysis along with field checking showed that 914 segments are marked as landslides anomaly over the area of 13578 ha. The maximum land sliding activities was identified as 1.58 meter vertical displacement during May 2010 to September 2011. Furthermore, results showed differential interferometry method applied for above mentioned frequencies has sufficient accuracy and conform efficiency for landslide detection, monitoring and distribution mapping compared to other methods (field survey in extend area, aerial photo and optical satellite images). Out of this two frequency, low frequency of PALSAR images has better ability in landslide zonation due to its capabilities such as longer wavelength and reduced incoherency. Where the high frequency of ASAR images can offer more details of the landslides due to its shorter wavelength.