Journal of Range and Watershed Managment
Year:2010 | Volume:63 | Issue:2|Papers Count:15

One of the most appropriate approaches for flood forecasting is using peak discharge data of hydrometric stations in each region. However, lack of such stations or short duration of data in most parts of the country, make it necessary to use some alternative methods in order to estimate the flood discharge properly. One of these approaches is regional flood analysis method that in a region using observation discharge data in separate points, it calculates relevant regional flood models. These approaches give us possibility at a region without gauging station with similar and homogenous hydrological condition to estimate flood discharge for different return periods with acceptable accuracy. In this research three methods of regional flood analysis including index flood, multivariate regression and hybrid method were considered in 20 watersheds of central Alborz region. After taking into account, the hypothesis and limitations of each method, the results were compared with observed flood discharges using RMSE and MBE. Considering the hypothesis and validation of multiple regression model indicated it is not appropriate. Finally Index Flood method in return periods of 2, 5 and 10 years and hybrid method in return periods of 50 and 100 years proved higher accuracy in the whole region and no difference between these two methods in return period of 25 were shown.

Desertification is the consequence of series of processes in which climate change and human activities are more important factors than others. Arid and semi-arid areas have occupied most parts of Iran. Sistan region is one of arid areas of Iran where wind erosion is an important factor of land degradation and soil deterioration. For classification of desertification intensity, several methods have been proposed so far. ESAs Model is on of the best and recent methodologies introduced by the European Commission in 1999 and evaluated by most of European as well as Middle Eastern countries. ESAs has more advantageous than other methods because of its accuracy, particular weighing of layers, use of geographical information systems in overlaying of maps, use of geometric mean over arithmetic one or sum in computing indices and final desertification map. The method was chosen to monitor desertification in the study area. The factors which affect on desertification were evaluated based on the related tables. According to the conditions of the study area, it was found that four factors including vegetation cover, soil, climate and land use management are the most important desertification factors. The results showed that climate play vital role in land degradation and desertification. Based on the results of it is found that the study area has critical conditions. It includes high critical (C3), moderate critical (C2) and low critical (C1) classes of desertification which cover 68%, less than 1% and 31% of the region, respectively.

Sistan plain is affected by desertification and this phenomenon has serious impacts on roads and socio- economic activities of local people of this region. The main purpose of this study is estimating the current and potential desertification intensity of Niatak region of Sistan based on MICD method. That, through it the working units of this region were prepared as the base map for evaluating to consider the factors and indices by geomorphology method. Also, in order to prepare the desertification intensity condition for both current and potential situations of this region, the desertification intensity of various applications was determined and relative plans to current and potential desertification of each land use were prepared after evaluating wind erosion indices and accumulating their scores for each working unit based on reference tables. The results showed that in this region the desertification potential consists of medium (III), intensive (IV) and very intensive (V) classes, while current desertification condition includes low (II), medium (III) and intensive (IV) classes of desertification intensity, respectively. These variations were resulted by wind erosion control activities over recent years.

Eremurus and forage are main by-products in the Khazangah rangelands of Makoo region. Eremurus is harvested and used by local people in a period of 30 days during the spring in this region. At this study, Eremurus and forage have been evaluated financially and the data were obtained through field work using unstructured interviews as well as direct observation. The harvested Eremurus value was estimated based on harvest costs and by means of market price. The data were analyzed through financial evaluation, annual present net value and infinite present net value or expected value. The results showed that gross revenue, economical rent and economical benefit per household were 4564 and 348 thousand Rials/yr, respectively. The amount of net benefit through harvested Eremurus was also 16748 thousand Rials/ha/yr. The Rangeland Expectation Value per hectare was estimated 670 thousand Rials/yr and 10.5 million Rials/yr from Eremurus and feed, respectively. Total Rangeland Expectation Value per hectare was estimated 11.17 Thousand Rials while the ratio of Rangeland Expectation Value of Eremurus to Total Rangeland Expectation Value was computed 6 percent. The rangelands of this region have much more products. Among them forage and Eremurus have been considered at this study. These products play a main role in local economy of the region.

The use of saline groundwater resources, in addition to save fresh water, could be used in production of forage in saline soils. In order to do it, the area in northern Ardakan, Yazd province with saline ground water (EC= 11.25 ds/m, SAR= 16.7) and saline and alkaline soil (EC=27.3 ds/m, ESP= 30.2%) was selected for planting of Atriplelentiformis, Seidlitzia rosemarinus, and Nitraria schoberi. The seeds of plants were collected from different areas of Yazd province, and were planted in nylon pots in greenhouse and transplanted as split plot statistical design in the field after one month. Based on the potential evapotranspiration of the region, the plants were irrigated as furrow design with leaching fraction (LF) = 0.3, and in 10 and 20 days intervals. After six months, plants were cut from near the soil surface and dried in oven at 60oC for 72 hours. The dry matter of each plant weighted and analyzed statistically.  The results indicated that there are some significant differences between dry matter of plants and the irrigation periods. Among plants, Atriplex lentiformis, with ten days period of irrigation had the best yield in this experiment. In addition, LF of 0.3 could decrease the salinity of the surface soil layers. This reduction was higher than in ten days period of irrigation.

There are large areas in arid regions having low rainfall and affected by land degradation due to change in environmental condition and anthropogenic activities (e. g. agricultural activities and misuse of the land). Consequently, these fertile lands were changed into degraded and bare lands. agricultural activities such as unwise management of the land as well as inappropriate irrigation systems in many parts of arid and semi-arid regions of Iran has seriously led to land degradation and desertification. So, it is necessary to do some research in order to determine whether the region is suitable for agriculture or not and if suitable what type of agriculture management should be applied prevalently? To achieve this objective Taleghan region located in Tehran province was chosen. Investigation on the effects of agriculture management systems on land degradation carried out in 4 stages. At first, collection of basic information, such as soil data, agricultural productions, area of farmlands and preparing the slope and aspect maps by Digital Elevation Model. Change of some factors such as EC, SAR, pH, N, P, K, and humus were also measured in soil surface (0-30 cm) according to split plot design. Six different series of soil were then recognized and 6 treatments with 6 replications including dry farming systems, mono- cultivated and multi- cultivated systems under irrigation, orchards, eroded lands and rangelands as control treatments were considered. The results showed that there were significant differences among treatments (agricultural lands). The comparison of treatments mean values with Duncan’s test indicated dry farming system and eroded lands as the most unsuitable treatments and multi cultivated lands as the most suitable one in this region.

The technique of relating areal rainfall depths to area by analyzing several storms gives depth- area relationships for different specific durations. So it is necessary to formulate maximum depth- area- duration curves to determine the maximum depths of precipitation from a given storm within various durations and areas. In this research, DAD curves have been prepared for Khorasan Province. There are more than 180 rainguage stations in the Province. Daily rainfall of these stations was collected from the beginning up to 2001 based on water years. For each year the number of days when the most stations having rainfall with the precipitation center station is determined. The investigations showed that there is only 14 days with more than 80 percent areal extension in the study area. Thus the rainy days with more than 50 percent areal extension and with 50 percent of stations having at least 5 mm rainfall, were selected as design storms. For drawing isohyetal map for each storm, GS+ software was used for determining the suitable interpolation methods. The mentioned maps were prepared using GIS for 41 selected maximum storms of the Province. Then the depth-area curves for each storm and final depth-area-duration curves were prepared for 3, 6, 9, 12, 18 and 24 hours durations. A mathematical model with the form of P/PM =[1-EXP (-a*Ab)] was fitted to area reduction factor curves, where P, PM and A are mean maximum areal rainfall, maximum point rainfall in the area in mm and watershed area in km2 respectively. The research showed that the accuracy of 18 hours DAD curve is less than the other of durations. It is recommended that the DAD and area reduction factor curves to be used only for areas between 10 to 30000 km2.

The main purpose of this research is presentation of a geostatistical index for indicating erosive wind direction in Hassan Abad. In this research main direction of prevailing wind was found by employing annual, seasonal and monthly wind rose diagrams while morphology of sand dunes and erosive wind directions are found by questionnaire.  The sampling was completed over sand dunes through forty sites over a regular grid (500 by 500 m) and after sieving, cumulative and scattered diagram of sand diameters are drown and mean diameter is calculated. Geostatistical studies were used for identification of spatial correlation (autocorrelation) of granolometric characteristics by variographic studies for identification of granolometeric continuity, range effect (radius of spatial correlation of grains) and spatial correlation anisotropy. In this study relevant and validated variogram demonstrated that the second-order stationary hypothesis is satisfied as well as the most spatial correlation is directed in azimuth of zero degree (direction of erosive wind). Geometric anisotropy analysis of region showed that the maximum diameter of anisotropy ellipsoid is parallel to erosive wind direction as well. Finally, mean diameter of sands is estimated in 50×50 meter blocks using ordinary kriging.

Increasing rate of land degradation and anthropogenic destructive influences have resulted in higher erosion and sediment yield. The determination of effective factors on erosion and sediment yield processes and determination of homogeneous regions considering these factors are then necessary for erosion and sediment yield management. In this study, by investigating sediment yield of 12 watersheds in the country, the most important factors on sediment yield were identified using Principle Component Analysis (PCA). Based on these factors, homogeneous regions were determined using Cluster Analysis. The results showed that three factors including De Martton Aridity Index, area percentage of erodible formations and vegetation cover have the highest influence on sediment yield. By using these factors three main homogeneous regions were introduced accordingly. These groups show the effective factors on sediment yield and their interactions very well.

Geomorphology try to show the environmental mechanisms and it helps human that artificial operations do not act against the environment. Actually, the skill of the geomorphologist is in recognizing natural morphodynamics factors. So it can forecast environment reactions before human operations and with this knowledge and wider vision can be successful in resolving of natural problems for cities. The geomorphologist can modify policies and guidelines and also planning of strategies to contact with environment. The urban geomorphology master plan is to identify lands and classify them according to natural hazards. In this paper natural hazards in the Bandar Abbes city has been identified and computed some parameters such as frequency, identity and forecast of occurrence abundance. This information was used to explain the quantitative aspects of natural hazards rather than the qualitative view. They are directly related to geomorphologic parameters. For this purpose, TOPSIS as one of the suitable tools for multiple criteria decision making and planning based on the Analytical Hierarchy Process (AHP) structure were considered. The results showed that in three regions of the city, the region number three has the maximum potential while the region number one has minimum potential in assessing geomorphic natural hazards. Generally hazards occurrence probability in the region number three is 2.9 times higher than the region number one. Also the maximum and minimum weights are related to earthquake and landslide in this region. Over past 10 years, this region has been affected by rapid urban development than other regions. Currently, the most expensive residential land is being sold in this region which means that, the most cost has been paid in the residential area with the highest natural hazard potential in the urban area.