Document Type : Research Paper
Authors
1 Assistant Professor, Soil Conservation and Watershed Management Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran
2 Researcher, Agricultural, educational and Natural Resources Research Center, Agricultural Research, Education and Extension Organization (AREEO), Zanjan, Iran
3 Associated Professor, Agricultural, educational and Natural Resources Research Center, Agricultural Research, Education and Extension Organization (AREEO), Fars, Iran
Abstract
Extended abstract
Introduction
Soil erosion causes land degradation and reduces their land fertility potential in watershed areas. Choosing the right methods and strategies for watershed management and designing appropriate soil protection programs for regional conditions is of great importance and identifying the main areas of sediment production plays a significant role in formulating these strategies. Gully erosion is one of the forms of water erosion and the intensified type caused by human activities and is one of the important factors of soil degradation that causes soil loss and sediment production in different regions of Iran. Today, gully erosion has received more attention than other forms of water erosion due to its importance and development caused by disproportionate human activities, and one of the reasons for this, is the share of sediment production between 10 to 94 percent in some worldwide studied watersheds. The extensive destruction of agricultural, pastural and residential lands, roads, gas and oil pipelines and relocation of villages are from other reasons for the importance of gully erosion. Despite of conducted surveys and many studies on Iranian gullies, still there is no accurate, comprehensive, and up-to-date information on the characteristics of gullies with respect to climate, land use, formation and soil type, sediment production, and economic damages. Therefore, this study attempted to prioritize them for planning management and conservation measures by studying gully characteristics in Qazvin Province and estimating their economic damages.
Materials and methods
The studied area covers the lands of Qazvin Province with an area of 15,559 km2. Its highest elevation is 4,061 m above sea level in the Shahroud Watershed and its lowest point is 275 m at the the Qezelouzn River in the Lower Tarom region. The average rainfall in the province is about 316 mm yr-1. Quaternary geological units include alluvial fan deposits and low-elevation river terraces, andesite and dacite volcanic tuffs, and Quaternary including alluvial fan deposits and high-elevation river terraces are the first three formations of the province with 392,000, 119,000 and 6,500 km2, respectively. The gully erosion areas of the province were identified according to the available information and referring to the relevant departments. Then, according to the initial identification, the accuracy of the gullies erosion locations was checked by field visits and the geographical coordinates of 24 gullies were recorded by GPS. Using the extensive Demarton climate map of the country, a climate map of the province was prepared digitally. In the next step, the maps of the gullies and the climate of the province were overlayed in a GIS environment and a map of the distribution of gullies in different climates of the province was prepared. From each climate, two areas with an area of more than 500 ha and three sample gullies from each area were selected as representative areas for field sampling and the dimensional characteristics of the gullies, soil, past and current land use, and economic damages from the expansion of gullies in the representative areas were measured. For each area, the type and the amount of damage resulting from the creation and expansion of gullies were determined based on the functional value of the land in fodder production (2.5 million Rials ha-1). Prioritization of gully erosion areas for watershed management and soil conservation operations was carried out based on the proposed method. First, the indices of area, length, width, depth, width-to-depth ratio, and damage amount indices were determined. Then, the value of each factor was divided by the average factor in the province and assigned to the region in ascending order, with a score of one for the lowest index value and a score of 10 for the highest value, and the prioritization of each factor was determined. Then, the sum of the priority scores of the indices was calculated and assigned in ascending order, with the highest score as the region with the first priority and the lowest score as the region with the last priority.
Results and discussion
The results of this study showed that gullies are distributed in all five climates of the province like cold semi-arid, super-cold semi-arid, temperate semi-arid, warm semi-humid, and warm Mediterranean, but they are more frequent and have more area in Mediterranean and semi-arid climates. Gullies in Qazvin Province have a general claw plan and a point frontal plan, which indicates the effect of surface runoff in their creation and expansion. Gullies are generally created at the bottom of valleys and have a greater lateral expansion and are located in the middle class (less than five meters) in terms of depth. The soil in the gullies has a heavy to semi-heavy texture and the lands are pastures. The economic damages on province's pastures due to the expansion of gullies has been estimated at 3,984 billion Rials. Gully erosion areas in Qostyn-Rud in the temperate semi-arid climate, the Abdareh with the cold semi-arid climate, and the Durchak in the warm Mediterranean climate are in the first, second, and third priorities for soil conservation operations, while Yalabad, Dastjerdeh, and Maallem-Kelayeh areas have lower priorities.
Conclusions
The economic damages caused to the rangelands of the province due to the expansion of gullies is estimated at 39.84 billion Rials. According to the results, based on the developed Demarton climatology, the Qostyn-Rud gullies in the temperate semi-arid climate, the Abdareh with a cold semi-arid climate, and the Durchak gullies in the warm Mediterranean climate are in the first, second, and third priorities for soil conservation operations, which can be used to make decisions regarding the allocation of funds and the implementation of soil conservation and watershed management programs. For more appropriate management of erosion and sediment caused by gullies in Qazvin Province, other plans should be implemented, such as the studying the impact of gullies on rangeland soil moisture and biomass production, the diversity of palatable and invasive rangeland species, the rate of gullies advancing in medium and long-term periods, and gully erosion prediction models, so that they can be managed more effectively.
Keywords
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