Iranian Journal of Watershed Management Science and Engineering
Year:2008 | Volume:2 | Issue:3|Papers Count:8

The purpose of this research was to investigate the farmer’s poll opinions toward soil conservation practices. The study consisted of all farmers in Karkheh and Dez watershed in Khuzestan (N=394), out of which 82 were selected through "proportionate stratified random sampling" method. The study was a descriptive - co relational, survey research. A questionnaire was designed and administered to gather the required data. A panel of experts verified its content validity. A pilot study was initially conducted to determine the reliability of the questionnaire. Findings in the study indicated that a majority of the farmers have positive attitude toward adoption of soil conservation practices. The results showed that there was a significant and positive correlation between farmers' attitudes towards adoption of soil conservation practices and level of using information resources and communication channels for acquisition of information regarding soil conservation practices and level of Cosmopoliteness. According to regression analysis the rate of using information resources and communication channels and Cosmopoliteness were found to have contributed to the increase of attitudes toward adoption of soil conservation among farmers in Karkheh and Dez watershed.

The role of rainfall in water resource management especially at arid and semi-arid regions is essential and generation of data for this hydrologic variable is very important step in a better water resources and agriculture planning. In this research for generating rainfall data in stations with limited data in Fars province, the method that proposed by some researchers in the year 1986 was used. In this proposed method for estimation of model parameters for generating rainfall data in stations with limited data, certain empirical relationships that exist between model parameters (Transitional probability from a dry day to a wet day, Transitional probability from a wet day to a wet day and gamma distribution function parameters (α andβ) that calculated in stations with enough data and some monthly average rainfall properties (Ratio of wet days and Amount rain per wet days) in the same stations was used. The number of stations with historical daily rainfall data was 9 that by use of data of these stations, general relationships for estimation of model parameters for generating daily rainfall data in Fars province were calculated. By use of these relationships, in 7 stations with limited daily rainfall data (5 years) daily rainfall data was generated. Results show that estimation of daily rainfall data by this simple method is reliable in comparison with observed daily rainfall data.

The precise streamflow estimation has importance in the planning of water resources management, the forecasting of the persistence of drought and the planning of reservoir operation. The lack of long term streamflow data in the most of rivers in Iran is an obstacle to suitable water resources management. The disaggregation method is one of the stochastic methods that are the useful tool in applicable hydrology. The reliable planning and design of hydrological systems need the generation of time series in smaller time scales and various sites. Through this method, hydrological variables can be disaggregated into smaller scales, either in temporal or spatial. The temporal disaggregation is the disaggregation of the annual time into series finer ones like monthly time series. The spatial disaggregation is the disaggregation of the annual discharge of Main River into the discharge of subbranches. In this research, the disaggregating of annual time series into semi-annual and monthly ones were carried out using basic and extended models and the spatial disaggregation were carried out using extended model. The streamflow of some branches of Ouromieh river basin have been used in this model.The results showed that the good agreement of the disaggregation models with normal streamflow series, the high accuracy of the extended results (using RMSE) and the preservation of the statistical properties (mean, standard deviation) between observed and disaggregated time series.

Flood events are the most destructive natural hazards which cause high damages to human being worldwide. In this case, our knowledge of the flood seasons and its geographical distribution and its magnitude can help us manage flood and reduce its hazard. In this study, flood season is determined for Halilrud basinusing Peak over Threshold (POT) and frequency analysis of annual peaks and selecting the 2-year return period flood as indicator. Log Pearson type III and 3-parameter Log Normal distributions were fitted to each station. Then, for seasonal flood analysis two graphical methods were applied. Both of these two methods showed two flood seasons to be sufficient for flood frequency. At last, the region was subdivided into two homogenous seasons based on flood seasons. The first group covers highlands with high rainfall and snow while the second covers the low land of the region.

Vegetation roughnesses coefficients are the main parameters used to determine river flow characteristics and are known to depend on the flow condition (depth and velocity) as well as vegetation condition (type and density). Flume experiments were conducted to investigate the vegetation density for submerged vegetation in river bed, banks, and flood plains.Artificial plastic plants (shrub type), were laid on the floor of a 14 meter long and variable slope flume facilitated in the Hydraulics Laboratory of the Soil Conservation and Watershed Management Research Institute (SCWMRI), for this study. The Manning's (n) values were estimated for different slopes, discharges, and flow depth and vegetation densities. The results reveal that the Manning roughness coefficient (n) increases as vegetation density increases, while it decreases when the flow depth and velocity increase and also showed that the roughness coefficient (n) isn't constant and is a function of the flow velocity and depth of water. Significant variation of the Manning's (n) value with flow and vegetation conditions urges the consideration of the flow and vegetation conditions in estimation of the Manning roughness (n). Three equations were developed for estimation of roughness coefficients for rivers and flood plains, with different states of vegetation density, flow depth and velocity.

One of the most important results of incorrect human activities in natural environment is the increasing of watersheds flooding potential that makes huge damages to the national resources of country every year. For this purpose, the response of Bagh-e-Malek catchment was calibrated, evaluated and simulated in a mathematical model using time-area diagram, hydrologic and topographic properties of the catchment. Then, spatial distribution of sub basins were determined in the catchment isochrones. In the next step, interaction between sub basins spatial distribution and flooding potential of the basin areas and their effects on generation peak flood were analyzed. These operations were modeled with assumption of flood control implementation in the sub basins located on each isochron. The results of this research indicate that the fifth isochron in Bagh-e-Malek catchment with area of 21.08 km2 has had the greatest impact on flood peak at the basin outlet. On the contrary, the sub basins located on isochron near the basin outlet have had less impact on flood peak. As a result, with concentrating on watershed management and flood control activities based on the prioritization on the sub-basins identified, a considerable decrease would be expected in implementation expenses of the flood control and river engineering projects.

This study was in the central part of Zanjan rood named basin Gomish abad, located between eastern longitudes of 47º 50' 56"- 48o 03' 52" and northern latitudes of 36º 58' 57"-37o 07' 29" using data obtained from aerial photo of 1956, 1967 and 2001, and Satellite images of 1990 and 1998 interpretation and field observations to locate the gullies. Then dataset were incorporated in Geographical information system with ILWIS. Remote sensing and regression analysis was applied to interpretate aerial photo and Satellite images of 1990 and 1998. Based on this, we selected 32 gullies and analyzed longitudinal growth of them during 1335-1383. The FAO method was selected as the most fitted method (among FAO, SCS and Thompson) for estimation of longitudinal development of gullies in the study area.

Gully erosion has an important role in decreasing the agricultural yield and income of the farmers in the regions under gully development due to higher sediment production than surface erosion and its impact on the faster drainage of water table and soil moisture. In this research, climates with gully erosion evaluated based on Dimarton method. From each climate, defined a specific area and selected 15 active and representative gullies for examination. Historical evidence including aerial photos, topographic maps, field and lab measurements were used to measure the area of gully erosion, area of different land uses including rangeland, dry land, irrigated cropland, length of roads, vegetation cover and soil characteristics. The correlation of gully erosion as a dependent variable with different land uses as independent variables was determined and analyzed using stepwise method in SPSS software. The results of the research revealed that the variation of the area of gully erosion had a positive and significant relationship in the 1% level with the area of bareland, area of dry land and length of roads and had a negative relationship with the area of rangelands. The results implied that suitable rangeland management and their exclosure would decrease the surface runoff and sediment dramatically.