H. Hesadi
Researcher of Soil Conservation and Watershed Management Research Institute, Kermanshah province, Iran.
Email: [email protected]
Kh. Jalili
Researcher of Academic Center for Education, Cultural and Research, Kermanshah Province, Iran.
Email: [email protected]
M Hadidi
Researcher of Academic Center for Education, Cultural and research, Kermanshah Province, Iran.
Email: [email protected]
Abstract
Soil losses in the world is one of main causes of fertility decreasing , sedimentation in canals and irrigation canals and rivers, decreasing of storage capacity in the dams ,increasing of floods frequency , environmental pollution and it prevents from stable development . Deficit in erosion data for quantity estimation in watersheds especially in watersheds with no measurement has caused that scientists and researchers to have a tendency toward to use of experimental methods for erosion and sediment studies. MPSIAC is one of known models that are used extensive due to suitable results.
In this model using nine factors that include surface geology, soil characteristics, climate parameters, run off, topography data, ground cover, land use, upland erosion and canal erosion and sediment transport and then estimate erosion and sediment yield. In the last decades applying of satellite data and geographical information systems helps to the scientists for gain better results in environmental studies based on capability of RS and GIS data tools conducted a case study on Kenesht watershed using MPSIAC and compared results with traditional studies .This study showed that separating homogeneous units is done better than traditional method, meanwhile the consumed time and costs new methods are very low. Results showed specific sediment yield range in homogeneous and hydrologic units is 1.92 to 26.09 and 3.45 to 5.37 ton/ ha/ year respectively. The amount of total sediment yield in homogeneous and hydrologic units in Kenesht watershed is 74305.47 and 66076.8 ton/year respectively; that show significant difference between traditional and new methods estimation.
Introduction
Soil erosion as “soil cancer” is a complex process and its multiple obvious and hidden social and environmental impacts are an increasing threat for the human existence (Ownegh, 2003). This phenomenon with decreased soil fertility cause the destruction of natural ecosystems like pastures, jungles and agricultural ecosystems (Bayramin , 2003) and Soil erosion rate is a key index for the assessment of land management strategies and sustainability of development programs of the countries (Ownegh, 2003).
Stable development of soil and water resources and effective life cycle, continuous productivity and premium of projects need correct estimation of elements and effective factors on soil erosion and the sedimentation of the regions (Barkhordari and Zaremehrjerdi, 2006). So complete knowledge and awareness of this phenomenon is vital. Expansion and presentation of qualitative relationship between the factors which are important for soil erosion is an essential need in soil erosion control (Nikkami, 2003).
Controlling and estimation of erosion intensify and sedimentation amount is essential for watershed management projects and determining the methods for fighting against this phenomenon in order to perform soil conservation programs and exact designing of erosion and sedimentation control structures is essential (Barkhordari and Zaremehrjerdi, 2005, Hadiane amri et al., 2006).
Obvious lack or shortage of statistics and information about soil erosion and sedimentation in many watershed areas because of lack of sediment measuring stations and high cost of such stations, using suitable experimental methods for the estimation of soil erosion and sedimentation reduction is very important (Refahi, 2004, Hadiane amri et al., 2006).
MPSIAC model is an experimental model for sediment estimation which has the ability to survey erosion and sedimentation in a qualitative and quantitative manner (Ahmadi, 1999).This model has been adapted for many watershed regions of storage dams in the Iran(Refahi, 2004) and is widely used in executive and research departments for erosion and sediment estimation(Nikkami,2003). Being a ware about the active nature of erosion and the calculation and drawings to reduce this process gives important information to specialists of soil preservation, designing dams, tankers, canals and resources management and damage estimation. Using this method in GIS is very easy so in most researches and studies this model is used to estimate erosion and sedimentation.
Jafari (2002) has performed a qualitative and quantitative estimation for the watershed area of Chiklhab by GIS and has estimated the criteria and scales necessary in PSIAC model and has used them in the above area.
Nikkami(2003) in a technical-practical and scientific journal about PSIAC in GIS environment has talked about main problems in implementation and usage of effective factors in the model and the correct and effective from this model in Iran. This research and similar researches which were done in Iran show that if we use the model and observing according to its conditions and criteria; the experimental models can give a correct interpretation about erosion and sedimentation in the watershed area.
Sadeghi (1991) in Ghezelowzan watershed area of Ghezelowzan showed that MPSIAC model for estimating erosion is a suitable method. Bagherzadeh karimi (1993) in the same area found that this method has the highest compatibility with the field studies. Jalalian (1992) showed that the estimated sediment by MPSIAC method has a good compatibility with the observed amount (Hadiane amri et al. 2006). nowadays, the speed of human beings a technology in gathering information and the need for quicker, more precise and more cost efficient factors decision making has caused the geographical information systems and remote sensing to be effective for productivity.
The use of GIS as a powerful tool in analysis and storage of data has greatly helped the increase of speed and accuracy of the studies and with the aid of satellite images and remote sensing techniques, we can have in time and orderly data for hard to reach places(Pilesjo, 1994). Same of the factors effective in erosion like land cover and land use can be extracted from satellite images (Gumel, 1996).
v So in this research by the use of remote sensing techniques and geographical information systems and applying MPSIAC as a good model in qualitative and quantitative erosion and sediment estimation the amount of soil erosion and sedimentation in Kenesht watershed in Kermanshah province was evaluated.
Material and method
The Kenesht watershed is located in the northern of Kermanshah in the west of Iran. It’s area is 14333.36 ha. The highest, lowest and average elevation of the area is about 3360, 1325 and 1837 m above mean sea level, respectively.
The average annual rainfall of area is 714.5 mm and annual temperature is 9.5?c. The general view of the watershed in its location in the country is depicted in figure 1.
Geologically the area under study is part of the metamorphosed zone of sanandaj-sirjan and includes the calsic stoned of Bistoon and the radiolarite stones of Kermanshah.
Geomorphologically the mountainous area covers a vast area, around 60% of area and about 15% as small hills and badland and river and alluvial fans and plains including about 25% of the area.
There are 9 types of plants in the area which are as fallows: two agricultural types, two rangeland types with Excellent condition and positive tendency, three rangeland types with good condition and fixed tendency, one type of rangeland with medium condition and fixed tendency and two range land types with weak and very weak conditions and negative tendency.
The research method
1- Preparing the maps and the necessary information
At first step the maps of geology, hydrologic units (fig.2), slope, land use, plant cover, soil and isohyet map was produced. Then these maps were overlayed and sediment homogeneous units map(fig.3) was defined to run MPSIAC model. Then with regard to existing relationship in the model we calculated the score for the nine factors of erosion and sedimentation and by the aid of GIS they were attached to sediment homogeneous units map. Further more the erosion rate map was produced using aerial photographs and satellite images and checked by the field control (fig.4). Finally in order to determine the runoff production potential of the area the hydrologic studies of Kenesht watershed was used.
2- Determining the sediment production in sediment homogeneous units and hydrologic unites
After preparing the final map of the potential erosion and sediment production in sediment homogeneous units, the amount of produced sediment in hydrologic units was calculated according to weight score of the sediment homogeneous units. The final aim of this research was the comparison of the derived results from sediment production potential estimation in hydrologic and sediment homogeneous units; so that the amount of specific sediment was calculated to compare the results.
The data analysis
For the comparison of the estimated sediments the data were analyzed in the following ways:
1- Sediment estimation and classification of produced sediment by sediment homogeneous units score.
The results of the model in each sediment homogeneous units analyzed. The results of these analyzes for homogeneous units are shown in table 1.
Table (1) The results of the analyzes for homogeneous units
After sediment estimation in each of the sediment homogeneous units and according to the table number1 sediment production estimation was done for the hydrologic units. The result of the calculation is shown in table 2.
Table (2) the calculations of the sedimentation in the hydrologic units with using the score of homogeneous score
After this with regard to the standard table of MPSIAC, erosion and sediment classes was determined according to the model and the result are summarily listed in table 3.
Table(3)Soil erosion classification and sedimentation rate in Kenesht watershed
By noticing the results of the model in sediment homogeneous units the estimated sediment yield was 74305.147 ton per year in Kenesht watershed.
2- The sediment estimation by using the model data according the score of hydrologic units:
The MPSIAC model was run in hydrologic units of the area under study as homogeneous units and calculated the produced sediment in each of the units. The results were shown in table 4.
Table (4) Sediment yield estimation in Kenesht watershed according to the hydrologic units units
After the estimation of the sediment production in each hydrologic units, soil erosion classes and sedimentation was determined according to the standard table for model MPSIAC and the result were summarily shown in table 5.
Table(5) Soil erosion classification and sedimentation rate in Kenesht watershed
With regard to the results of the model execution in hydrologic units, the sediment yield of the area is estimated at 66076.18 tones per year in Kenesht watershed.
Conclusion and discussion
MPSIAC model is used widely for qualitative and quantitative estimation of soil erosion and sedimentation in executive and research units. There are main problems in the use of this model. One of the biggest problems is using the inhomogeneous area for sediment estimation (Nikkami, 2003).
In order to investigate this matter Kenesht watershed area of Kermanshah which by meeting the criteria in the model and the suitable conditions, 184 homogeneous units was found and MPSIAC model was performed in each of the units.
The results showed that the amount of sedimentation in each homogeneous unit was estimated 1.92 to 26.09 tones per hectare and the specific sediment of Kenesht region is 5.18 tons per hectare per year and the sediment yield of the region was 74305.47 tons per year. But the performance of the model in hydrologic units as homogeneous area (traditional method for use of MPSIAC model) showed the produced sediment is between 3.45 to 5.37 tons in hectare per year and the specific sediment of the region is 4.61 tons in hectare per year and the sediment yield of the region is estimated at 66076.80 tons per year. Also the specific sediment distribution of the hydrologic units by the use of the estimation method of the sediments in homogeneous units is 3.13 to 8.36 and with the use of hydrologic units it is 3.45 to 5.37 tons in hectare pre year.
Comparing of the above values shows that the performance of the model for sediment estimation in homogeneous units is better than traditional method. Distribution of sediment yield and its amount in each homogeneous unit is exactly and sediment production range is from 2 to 26 tons per hectare. But the estimated specific sediment of the hydrologic units as homogeneous units is 3.45 to 5.37 tons per hectare per year and shown an average sediment production and does not show careful distribution of erosion and sedimentation.
After the estimation of the sediments in each of sediment homogeneous units we classified the soil erosion and sedimentation amount according to MPSIAC models to erosion class 1 (very low) and II (low) didn’t exist and the average sedimentation was classified as very high noticing table 2 shows that 37% of the whole area has an average potential of sediment production and 8% of the region’s area has a very high potential of sediment production. 55% of the region was classified as high class of sedimentation areas.
The classification of potential of soil erosion and sedimentation in hydrologic units showed that only 3 percent of the region’s area has low potential of sediment production and the rest of the region has an average potential of sediment production.
The comparison of the qualitative soil erosion rate of the region with the maps of sedimentation rate from performing the model in sediment homogeneous units (fig.5) and hydrologic units (fig.6) shows that there isn’t a great difference between the qualitative erosion rate map and sedimentation rate intensity distribution map gotten from sediment units. But it is very different from the sedimentation rate map in hydrologic units.
Acknowledgements
The authors profoundly are grateful to Kermanshah Academic Center for Education, Cultural and Research (ACECR) and the general governor’s office of Kermanshah Province for supplying valuable information and assistance.
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