IRANIAN JOURNAL OF WATERSHED MANAGEMENT SCIENCE AND ENGINEERING
Year:2007 | Volume:1 | Issue:2|Papers Count:8

In this study, the main aim was to investigate the sediment transport mechanism in ephemeral rivers due to flash flood using an experimental research work undertaken in a tilted laboratory flume. Since during a flash flood phenomenon, flow is generally in unsteady conditions, a reservoir tank was installed at the upstream of the flume to produce various forms of hydrographs of unsteady flows with different magnitudes of discharges and base times. Fine and uniform sand with of 1,5 mm was used as the mobile bed simulation. For the same maximum discharge (hydrograph peak), the results show that sediment transport was increased for the shorter of hydrograph base time. The amount of sediment load for the unsteady conditions was more than the corresponding value for uniform flow with this being due to the effect of dynamic wave and its amount is as a function of wave conditions. For hydrographs with longer base time, the amounts of sediment load were found to be close to the values obtained for the uniform conditions. The gradient of increasing discharge in hydrographs was found to be the predominant parameter in sediment transport load. Bed deformation from the primary wave was significant and as a result bed resistance was notably increased. 

Design Flood can be accessed through frequency analysis method by using probability principles and existing data. Short statistical series or missing data cause extrapolation uncertainty in appropriate assessment of design flood. After accomplishment of studies for Jareh Reservoir Dam in Ramhormoz, big floods to the extent of discharge design of its spillways have occurred. Applying these data in flood series has caused remarkable changes in design flood. The objective of this research is assessment and evaluation of design flood of a reservoir dam based on flood statistical series. In this research, along with completion and evaluation of statistical accuracy of instantaneous maximum flood series, frequency analysis method has been used for assessment of design discharges. Flood Index Method has been used to determine flood hydrograph. The results indicate that the increase in magnitude of flood statistical sample not only changes the type of data statistical distribution, but also have a great impact on flood estimated values. This study shows an increase of 97% in peak discharge of spillways. The major differences refer to an increase of number of observations and magnitude of occurred flood events. The results of this research are useful in Jareh Dam as well as design flood assessment of other dam development projects within the basin and the adjacent ones.

Today, studying climatic variations with respect to different climate variables such as precipitation, evaporation, temperature, and air pressure in various parts of the world is important. This topic has received more attention especially in areas with intense wet and dry periods for water resources and crisis management. In Southeast of Iran, especially in Sistan & Baluchestan Province, very intense climatic variations have been observed in recent years. Various methods for clustering clustered signals have been developed, which are suitable for modeling of climate variations in such areas. In this paper, a new method for clustering satellite information of Sea Surface Temperature (SST) using Genetic Algorithm Clustering is presented. Different parts of this research are based on selection of best model framework, objective function, length of chromosomes and mutation and crossover operators. This model tries to find the relation between SST data and above and below normal precipitation. 20 rain gauges in Sistan & Baluchestan Province have been considered in the case study. Using the Genetic Algorithm for mapping, the relation between precipitation in various seasons and temporal-spatial clustering are innovative aspects of this paper. The results show the potential of using the clustering method for forecasting the seasonal behavior of precipitation in Southeast of Iran.

Estimation of flood discharges are required for design of hydraulic structures, floodplain zonation and watershed management works. It is required to extend the regional flood models based on station data to ungaged locations within the same region. The spatial variation of drainage area as the main variable in regional models may be determined by GIS. Therefore, having the regional model and the corresponding maps of independent variables, one may extend the model onto the rivers. Specific attention is given to the role of GIS for model's spatial extension, derivation of flood maps and extraction of flood profiles in rivers.Another word, the methodology of spatial extension of regional flood analysis based on data of hydrometric stations is the main problem in this paper.The discharge data of 22 watersheds in Gilan province were regionally analyzed. Independent variables such as area and slope were extracted based on the digital elevation model (DEM). Map of average annual rainfall was also prepared for the region. A program for spatial mapping was written in Arc View GIS.This program uses D8 flow tracing algorithm to identify the upslope cells of a given target cells. Average values of independent variables such as slope and rainfall is determined by having the upslope cell values.Thus, it is possible to compute flood discharge at the ungaged target cell using the regional model equation which involves the average values of independent cells. As such, the flood map in river cells is extracted.One can use these maps to study the variation of flood discharge along the river length. Finally, the share of each independent variable in the regional flood model was investigated. The methodology to prepare the base flood maps are the most important outcome of this paper which may be used in design of hydraulic structures as well as flood control measures.

Landslide is one of the mass movement processes that occur in Iran and parts of the world every year. It causes huge human loss and economical damages. This research investigates the evaluation of fuzzy logic operators in prediction of landslide potential. Thus, Shirood Watershed was considered as a suitable model for north of Iran. First, investigating resources, some of the most important factors in landslide occurrence such as slope, litho logy, land use, aspect and distance from fault in G.I.S. environment were prepared and digitized as independent variables. Landslide distribution information layer was prepared with use of interpretation of air photos and field survey with use of G.P.S. variables. The classification was done with histogram trend changes and available classifications. Weighting variables classes were determined between 0-1, and then weighted maps classified with fuzzy operators. Obtained maps accuracy was evaluated with use of quality sum index (Qs)' Results showed the fuzzy Gamma 0.8 operator is one of the best suitable operator for land slide potential in Shirood Watershed.

Over the past century various equations have been proposed to predict the velocity and depth of uniform steady overland flow of water. The three most widely used expressions being these of Darcy-Weisbach, Chezy and Manning. The magnitude of resistance coefficients in equations such as those of Darcy- Weisbach, Chezy or Manning vary with flow velocity (at least). Using both original laboratory and field data, and data from the literature, the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity, even in the absence of interaction between hydraulics and resulting erosion of bed forms. Resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources. The result is that Manning's equation received stronger support than the Darcy-Weisbach or Chezy equations, though all equations were useful. The second question addressed is how best to estimate velocity of overland flow from measurements of slope and unit discharge, recognizing that the apparent flow velocity variation in resistance coefficients is probably a result of shortcomings in all of the listed resistance equations. A new methodology is illustrated which gives good agreement between estimated and measured flow velocity for both well-inundated sheet and rill flow.Comments are given on the predictive use of this methodology.

Determination of drought resistance various species of trees and shrubs species in different regions is very important. The Leaf Water Potential (LWP) is the best Physiological parameter that with presentation of status water in plants, we can recognize the drought resistance species. Therefore this study was designed to recognize the drought resistance species according to their Predawn leaf water potential (PLWP) on 20 plants species of trees and shrubs in two forest regions, Arasbaran in Azarbayejane Sharghi province and Hosseinabad in Ghazvin province. After field revisions, the florestic list of plant species in both of regions provided and then LWP of Acer campestre, Carpinus betulus, Comus' australis ,Comus mass, Comus sunjuineas, Crataegus spp, Fraxinus rotundifolia, Quercus macranthera, Quercus komoravii, Salix alba and Ulmus glabra species in Arasbaran county and Acer campestre, Comus australis, Comus mass, Fraxinus excelsior, Fraxinus rotundifolia, Lonicera iberica, Populus nigra, Salix alba and Sorbus umbellata species in Hosseinabad county were measured. The measurement time in summer and spring days was at 13 - 15 PM in 2005. The data in per region analyzed separately. The result showed that there were significant differences between the plant species for the LWPamount. According to the results in Arasbaran regions Crataegus spp (-3.5 MPa), Fraxinus rotundifolia (3.2 MPa) and Quercus macranthera (-2.75 MPa) species were the most drought resistant and Acer campestre (-1.2 MPa) and Carpinus betulus (-1.75 MPa) species had lower drought resistant. Also in Hosseinabad Fraxinus rotundifolia (-3.3 MPa), Lonicera iberica (-2.85 MPa) and Quercus macranthera (-2.9 MPa) species were the most drought resistance and Populus nigra (-1.48 MPa), Salix alba (-1.6 MPa) and Acer campestre (-1.9 MPa) species had lower drought resistant. In general the experimental results showed that we can select species with high drought resistance potential to introduce them for urban greeneries and forestry in arid and semi-arid regions.

Drought is universal phenomenon that can occur everywhere and can cause harmful impacts on human beings and natural ecosystems. Thus it is very important to study drought. In this study, the Standardized Precipitation Index is used for regional drought analysis in Isfahan Province. In this study, after collecting the precipitation data in all Isfahan stations and removing those stations with incomplete data, SPI time series were calculated in different time scales of 3, 6, 9, 12 and 24 months. Then, frequency of drought extension's maps (in 12 months time scales) was prepared and analyzed using Geostatistics methods (Kriging). These schemes show moderate and severe drought mainly in the West regions of the province, I in the areas neighboring to Fereidoonshahr, Daran and Fereidan cities. They also show extreme droughts in the East and North East regions of the province with high drought risk and necessity for better future it planning and management strategies in these regions.