IRANIAN JOURNAL OF NATURAL RESOURCES
Year:2002 | Volume:55 | Issue:1|Papers Count:12

Among the main objectives in hydrology are to quantitively forecast the process of rainfall–runoff, and to determine flood discharge at the outlet of a watershed. Flood discharge can be estimated using rainfall-runoff models which explain hydrological phenomena for ungaged watersheds. If the dimensions of flood hydrograph (which is the result of the watershed response to rainfall) are known, then the importance of models which are based on geomorphology of a basin will be very clear. The purpose of this study is to investigate the consistency, accuracy and reliability of geomorphological and geomorphoclimatical models in estimating the shape and discharge of flood resulting from a rainfall with certain intensity and duration. The results of these two models were compared with Nash, Rosso and SCS models. The results showed that the efficiency of geomorphologic model ratio to geomorphoclimatic, Nash, Roso and SCS are 106.56, 171.12, 106.79 and 112.64 percent respectively, and that geomorphoclimatic model ratio to Nash, Rosso and SCS is 106.57, 100, 21 and 105.69 percent, respectively. Therefore, the result of geomorphologic model compared to other models (based on this study) is the most efficient model to estimate flood discharge.

Paleoclimatic investigation of the Quaternary period reflects fluctuation in climatic conditions during geological periods. Abrupt climatic changes, viewed as problem causing global incidents bring about adverse side effects in sensitive climatic zones such as Iran. Droughts and unpredictable floods that damage natural resources as well as human life become common yearly occurrences. Apart from influences of natural physical factors, human activities, if not properly controlled, add to the destructive power of the floods too. This happened in the Nekaroud basin mainly due to deforestation and damaging changes in landuse during the last century. The huge magnitude flood of summer 1999 which caused irreparable downstream damage and death of citizens is a sad incident of such environmental changes. The present study is an investigation into some characteristics of Nekaroud basin, an analysis of the reasons behind the occurrence of the catastrophic flood, ways to predict and prevent similar disastrous incidents in other catchments basins in Mazandaran as well as in other regions with similar conditions in Iran.

Suspended sediment yield data could be used for estimating soil erosion in drainage basins. The objective of multiple regression analysis is to use the independent variables (values known) to predict the single dependent value selected by the researcher. In this research, eleven stations were selected in Gorganroud drainage basin according to area of upland catchments, geology, climate, vegetation cover, etc. The potential factors effective in suspended sediment yield were identified. Using the mean load within discharge data, 30 years mean suspended sediment load of each station was estimated. Multiple regression analysis was used to obtain the best statistical relationship between suspended sediment yield data and independent variables. According to the final model, the percentage of forest area density and mean annual discharge varies together and are in positive relationship with sediment yield. Inversely, the percentage of area of resistance and relatively resistant geological formation has negative effect on sediment yield. These three independent variables explain more than 96% of variation in mean suspended sediment load in Gorganroud basin and exhibit 19% standard error in their prediction.

Increasing the seed germination capacity of Service tree (Sorbus terminalis) in a mountainous tree nursery was the main goal in this research, which was carried out in Orimelk nursery, located at 1550 meter altitude, Northern side of Farim Forest in north of Iran. In order to suggest the most suitable method of seed sowing for this species in mountainous nursery, three treatments of sowing depth including 1.5, 2.5 and 3.5 centimeters and two treatments of soil surface protection (with and without mulch) were studied using factorial experimental design in three replications. Analysis of variance showed a significant difference between the two levels of soil protection factor at 0.01 level of probability. The average number of emerged seedlings in the coverd plots was two times greater than the other one while, germination rate was not significantly different among the sowing depths of covered plots, but there was a significant difference among the three depths of uncoverd plots. In other words, the deeper the sowing depth, the more the number of seed germination. Duncan multiple range tests grouped together all three depths of the covered plots and 3.5 cm deep uncovered whereas the rest of the treatments were grouped together.

In this study, the possibility of making tannin-formaldehyde adhesive from the bark of oak, beech, alder and hornbeam was investigated. The bark mixture was extracted using polar and non-polar solvents. Samples of tannin-formaldehyde and phenol-formaldehyde adhesives were prepared at pH 9.5 with molar ratio 1:2, and the viscosity of the samples was measured following D2556 ASTM standard method. By measuring the shear strength of plywoods made with new formulations, the strength of the products was evaluated, following Iranian Standard No.3492. The experimental results show that quantitatively, 1% NaOH solution is the most efficient extracting solvent. However, the purity of tannins and phenolic compounds is highest when extracting solvent is ethanol. Also, the shear strength of adhesives soluble in alkali is better than adhesives soluble in other solvents. The shear strength of the samples could be doubled when adding 25% phenol to tannins compared to urea-formaldehyde adhesive.

Azolla filiculoides Lam. is a free-floating weed, which has occupied a vast surface in Anzali lagoon. Excessive growth of Azolla on the surface of Anzali lagoon has not only interfered with the use of the lagoon as a water resource, but has also created ecological and water quality problems. To determine the reasons for Azolla excessive growth, four experiments were undertaken under laboratory conditions, fish pond and Anzali lagoon during years 1999-2000. Experimental results showed that Azolla with a more rapid growth and a lower doubling time was the superior competitor when in competition with Lemna minor. The research revealed that maximum relative growth rate (0.11gg-1 day-1) and minimum doubling time (6.27 days) were observed during May and June respectively. Results indicated that by raising the temperature from 18 to 21 and from 21 to 24C° in 20mg Po4-Pl-1 a significant increase in growth rate and substantial decrease in doubling time were obtained. Experimental results showed that 2 applications of paraquat herbicide with 0.75, 1.25 and 1.5 mg l-1 under laboratory conditions, fish pond and Anzali lagoon, respectively and significantly reduced the biomass (plant dry weight) stopping the growth. The growth rate and doubling time record for Azolla in this investigation illustrates its rapid colonizing ability. Thus, a small amount of Azolla present in the Anzali lagoon has the potential to spread rapidly and cause serious weed problems. The cessation of the sewage inflow to the lagoon and using a contact herbicide such as paraquat with suitable dosage were the necessary steps to significantly reduce Azolla growth.

This study was carried out to investigate the effect of ecological and geomorphological factors on establishment of plant communities in Chenar Rahdar region of Fars province, with an area of 31,790 hectares. The studies of physiography, climatology, geology, lithology, geomorphology, and phytosociology were conducted. Using aerial photographs as well as slope, aspect, altitude, lithology, and geomorphology maps, uniform work units were determined. Considering Braun- Blanquet-Kuchler method (Floristic-physiognomic method), separation and classification of plant communities were done in each uniform work unit. According to some vegetative characteristics such as storey, density, and life form and then using color patterns and numbers each plant unit was shown on the vegetation map with its physiognomic formula being defined. Results showed that the plant communities established in the mountain unit, were mainly affected by climate while in hills and high grounds, soil was the effective factor. In those parts of the study region where degradation was lower, there was a close relation between the geomorphological faces and plant communities. On the homogenous geologic formations, the variety of plant communities depended on the elevation while population was influenced by slope and aspect. Among different soil characteristics, texture, depth of horizons, sand hardpan, and the amount of gypsum and lime played the most important role in determining the plant communities.

Relationship between plant and soil is of special importance because it is possible to establish a judgment on one by considering the other. This research was carried out to find the relationship of vegetation cover with soil physical and chemical characteristics in semi steppe rangeland of Mehrzamin region in Qom province. According to the distribution of vegetation cover and based on field surveys, nine vegetation types were distinguished. To study vegetation in each type, fifteen 1m2 quadrates were established. Within each quadrate, canopy cover belonging to each species was recorded. For each dominant species, four profiles were dug and soil samples being taken from two topsoil and subsoil horizons. In the next stage, soil characteristics such as pH, Ece, CaCO3, amount of potassium, organic matter, rock and pavement as well as texture were determined in a soil laboratory. After collecting the data, multiple regression analysis, correlation coefficients and factor analysis were done or obtained using SPSS Win, Mstat and SAS software packages. The results of simple correlation coefficients and stepwise multiple regression analysis of soil properties with cover of dominant plant species showed that among different soil properties, depth of horizon and amount of potassium exhibited the highest correlation while electrical conductivity was of the lowest correlation with dominant plants’ crown cover.

Vegetation mapping is one of the important aims phytosociologists are after. Ever-increasing improvement of satellite images in terms of their spatial and spectral resolution made them suitable for vegetation mapping. Satellites capture electromagnetic radiation reflected or emitted by objects on the earth. Electromagnetic radiation itself is a function of spectral property of the object, sun position (sun azimuth and elevation), and surface terrain. As a result, a given plant cover on different aspects of the terrain may be detected differently. This is especially true for images from mountainous environments. Thus, it is necessary to use techniques that can improve the amount of information obtained from such images. Several such techniques have evolved over the years, including the odeling of illumination effects using a DEM2 and the calculation of surface roughness index such as Minnaert constant to adjust over correction caused by non lambertian models. This research attempts to apply such method to study the effects of topographic normalization on classification accuracy of Landsat TM image acquired for the preserved mountainous area of Jahan-nama in province of Golestan. The study area was classified using MLC3 method on images, which had been topographically normalized by applying Minnaert constant. The results of comparing topographically normalized thematic map with original thematic map show that the topographic normalization method applied over corrects the image, and that the overall classification accuracy on corrected image is lower than the uncorrected one. The over-correction seems to be due to the quality of DEM used in the procedure. Using the information about the sun position which is available from the Landsat header file, is probably the other source of over-correction. This is because it is the position of sun relative to the center of the image while the study area was located at the extreme end of the image. The research suggests that calculating the position of sun for all pixels involved may help deriving better results.