نوع مقاله : مقاله پژوهشی

نویسندگان

• منصور جهان تیغ
• معین جهان تیغ

بخش تحقیقات حفاظت خاک و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی سیستان، سازمان تحقیقات، آموزش و ترویج کشاورزی، زابل، ایران.

چکیده

این پژوهش با هدف بررسی اثر عمق رسوبات مخازن بندهای خاکی بر توزیع اندازۀ ذرات و نفوذپذیری خاک بندهای احداثی در غرب منطقۀ سیستان اجرا شد. تیمارهای مورد مطالعه شامل سن بند (18 و 22 سال بعد از ساخت)، عمق برداشت (صفر، 15 و 30 سانتی‌متر) و سطوح برداشت (پای بند، 25، 50 و 75 درصد) بودند. با استفاده از روش استوانۀ مضاعف میزان نفوذپذیری و با نمونه‌برداری از عمق های خاک برخی ویژگی­ های فیزیکی نمونه‌های برداشتی در تیمارهای مورد مطالعه و منطقه شاهد تعیین شد. نتایج تحقیق نشان داد که میزان سرعت نفوذ در عمق‌های مختلف برداشت رسوب اختلاف معنی­داری نشان می ­دهد و کمترین و بیشترین میزان نفوذ‌پذیری به ترتیب مربوط به افق سطحی و عمق 30‌ سانتی‌متری رسوبات برداشت شده است (به ترتیب 1/52 و 2/34 سانتی‌متر بر ساعت). در بررسی اثر رسوبات تجمع یافته بر توزیع اندازۀ ذرات خاک، یافته‌ها نشان داد که درصد رس، سیلت و شن در خاک مخازن بندهای خاکی تفاوت معنی‌داری نسبت به منطقۀ شاهد در عمق‌های نمونه‌برداری دارد، به ­طوری­که درصد رس و سیلت به ترتیب 14/2 و 3/2 برابر نسبت به منطقۀ شاهد افزایش یافته است که به تبع آن باعث تغییر بافت خاک از کلاس شنی (منطقه شاهد) به لومی رسی در مخزن بندهای خاکی شده است. تغییرات شاخص میانگین وزنی قطر خاکدانه‌ها (MWD) در تیمارهای مورد مطالعه نیز بیانگر کاهش محسوس این شاخص در مخازن بندهای خاکی نسبت به منطقۀ شاهد بود. نتایج حاصل از تحلیل رگرسیون چندگانه به­ منظور تعیین مهم­ترین عوامل مؤثر بر نفوذپذیری خاک نیز بیانگر آن است که مقادیر شن 96 درصد تغییرات نفوذپذیری خاک را در تیمارهای مورد مطالعه توجیه می‌کند. بر اساس نتایج این تحقیق، تجمع رسوبات در مخازن بندهای احداثی با تغییر ویژگی­ های فیزیکی و شاخص‌ پایداری خاکدانه‌ باعث کاهش نفوذپذیری خاک این مخازن شده است که بهره‌برداری از این رسوبات ضمن افزایش کارایی این بندهای خاکی بستری مناسب برای اصلاح زمین­ های سنگلاخی و سنگریزه‌ای پایین دست فراهم می­ کند.

کلیدواژه‌ها

• تغذیۀ مصنوعی
• رسوب
• سیلاب
• نفوذ آب در خاک
• ویژگی‌های فیزیکی خاک

موضوعات

• منابع و مصارف آب

عنوان مقاله [English]

The effect of sediment depth in recharging earthen dam reservoirs on particle size distribution and permeability changes in arid regions (Case study: West of Sistan)

نویسندگان [English]

• Mansour Jahantigh
• Moien Jahantigh

Department of Soil Conservation and Water Management, Sistan Agriculture and edition Natural Resources Research Center (AREEO) Zabol, Iran

چکیده [English]

Extended Abstract
Introduction
       Currently, water shortage is one of the challenges that has affected many regions, especially arid areas, due to population growth and irrational and unscientific use of water. So that excessive use of water from wells, the groundwater level has been lowered significantly, resulting in a decrease in the water flow of aqueducts and wells, and even the loss of some of these water resources. In order to solve the problem of water scarcity for various purposes such as providing agricultural water resources, permeability water into the groundwater table, increasing the vegetation cover, improving the environment, etc., earthen dams have been constructed in some susceptible areas, including arid regions. However, sedimentation in the reservoirs of these structures and subsequent disruption of the rate of infiltration into the ground is one of the problems that the construction of such dams brings. On the other hand, the factors that disrupt the infiltration of water into the groundwater table are sedimentation in the reservoirs of these earthen dams, which in some places turn into evaporation ponds due to the accumulation of sediment inside their reservoirs. Sedimentation of materials inside dam reservoirs is the result of sedimentation of materials carried by tributaries and reduces their permeability capacity. The intensity of this sedimentation process depends on the roughness of the watershed, its use, soil types, and the intensity and duration of rainfall. The type and location of the reservoir, as well as the hydrological regime of the river, also play an important role in this regard. So that their capacity may be reduced by up to 80 percent and cause the reservoir to lose its water storage function. In addition to the fact that these sediments play an effective role in reducing the volume of reservoirs, another important aspect is their pollution. The chemical composition of the sediments depends on the type of soils in the watershed, their agricultural use, and also the type of industry in the region. Considering that Sistan is one of the regions facing a water crisis and that numerous earthen dams have been constructed in its western highlands, there is a need to investigate the performance of these structures regarding their permeability status with the witness area so that, if necessary, reforms can be made for their optimal exploitation. Therefore, this research was conducted in the reservoirs of dams constructed in the western highlands of Sistan.
 Methodology
To carry out this experiment, five earthen dams in the region, which were constructed in the 1970s, were selected and the amount of aging infiltration from the reservoir of these constructed dams and the control area was measured at different depths based on the standard double cylinder method at different times. By sampling the soil of the studied treatments, the physical properties of the soil samples were also determined.
Results and Discussion
The results showed that the infiltration rate in the control area was on average 1.2 times higher than the reservoir of the constructed dams, which showed a significant difference at the one percent level. In addition, the cumulative infiltration of the control area was also higher than that of the dam reservoirs and was statistically significant at the 5% level (p ≤ 0.05). In examining the effect of accumulated sediments on soil particle size distribution, the findings showed that the percentage of clay, silt, and sand in the soil of earthen dam reservoirs had a significant difference compared to the control area at sampling depths (p ≤ 0.05). The percentage of clay and silt increased by 14.2 and 3.2 times, respectively, compared to the control area, which consequently caused a change in soil texture from sandy class (control area) to clay loam in the earthen dam reservoir. Changes in the weighted average diameter (MWD) index in the studied treatments also indicated an 18-fold decrease in this index in the earthen dam reservoir compared to the control area. The results of multiple regression analysis to determine the most important factors affecting soil permeability also indicated that the percentage of sand accounted for 96% of the changes in soil permeability in the studied treatments.
 Conclusions
       The construction of an earthen dam increases the recharge of underground aquifers, which has a favorable effect on the water supply of wells and aqueducts, which in turn plays an effective role in increasing employment generation, improving the living conditions of watershed residents, and reducing their socio-economic problems. However, due to the lack of proper management of the sediments accumulated in the reservoirs of these dams, after several floods entered the reservoirs of these dams, their permeability has decreased significantly, and after a few years of water withdrawal, their reservoirs have become evaporation ponds, and a large part of the water entering these reservoirs evaporates and becomes unavailable without being used. The results of this study also showed that with the accumulation of sediments resulting from the entry of floods into these areas and the change in the physical properties and stability indices of soil aggregates, the permeability of these areas has decreased significantly. In addition, with the accumulation of sediments in the reservoirs of dams and their rising levels, their overflows are easily destroyed, which has led to the intensification of water erosion in the studied areas.
Keywords: Artificial infiltration, Flood,  Sediment, Soil physical properties, Water penetration into the soil.
 Acknowledgement
The authors would like to thank all participants of the present study.
Conflict of Interest
The authors declared no potential conflicts of interest concerning the research, authorship, and publication of this article. Confirmation.
Funding
The authors received no financial support for the research, authorship, and publication of this article.
Data Availability Statements
The datasets generated and/or analyzed during the current study are available from the corresponding author on reasonable request.
Authors’ contribution
Authors have read and agreed to the published version of the manuscript. Authors contributed equally to the conceptualization of the article and writing of the original and subsequent drafts.

کلیدواژه‌ها [English]

• Artificial infiltration
• Flood
• Sediment
• Soil physical properties
• Water penetration into the soil