نفوذ عمقی رسوب و اثرات آن بر خصوصیات فیزیکی و شیمیایی خاک در پخش سیلاب کاشمر

علاوه بر کمبود بارندگی، وقوع سیلاب های شدید از ویژگی های اقلیمی مناطق خشک و نیمه خشک است. رسوبات موجود در سیلاب ها موجب تغییر ویژگی های فیزیکی و شیمیایی خاک می شوند. در این تحقیق آثار پخش سیلاب بر خصوصیات فیزیکی و شیمیایی خاک سطحی و عمقی کانال های پخش سیلاب کاشمر بررسی شد. از اعماق 500 و 10050 سانتی متری از سطح خاک پنج کانال ابتدایی پخش سیلاب و عرصه ی بالادست آن به عنوان شاهد نمونه برداری شد. درصد شن، ماسه و رس و مقدار ec، ph، بی کربنات، سولفات، کلر، پتاسیم و سدیم در آزمایشگاه تعیین شد. نفوذپذیری خاک با استوانه های دوتایی اندازه گیری شد. تجزیه و تحلیل آماری نمونه ها در قالب طرح بلوک تصادفی سیستماتیک و مقایسه ی میانگین ها با استفاده از آزمون دانکن انجام شد. نتایج نشان داد میزان نفوذپذیری در بین کانال ها در سطح احتمال 1% تفاوت معنی دار دارند. به طوری که کانال های 1 و 2 با کمترین نفوذپذیری در یک گروه و کانال های 3، 4، 5 و عرصه ی شاهد با نفوذپذیری زیاد در گروه دیگری قرار گرفتند. درصد شن، سیلت و رس در عمق 50 سانتی متری خاک تفاوت معنی داری در سطح 5% بین کانال های عرصه ی پخش و شاهد نداشتند. مقدار ph در عرصه ی پخش نسبت به عرصه ی شاهد افزایش معنی دار و مقدار ec، بی کربنات، کلر، سولفات و سدیم کاهش معنی دار در سطح 1% داشتند. مقدار پتاسیم خاک در عرصه ی پخش نسبت به شاهد تفاوت معنی داری در سطح 5% نداشت. به طور کلی پخش سیلاب، نفوذپذیری خاک کانال های پخش را بیشتر تحت تاثیر قرار داده است و بیشترین تغییرات فیزیکی و شیمیایی در خاک سطحی اتفاق افتاده است.

The Deep Infiltration of Sediment and Its Effects on Physical and Chemical Properties of Soil in Kashmar Flood Spreading

IntroductionIn arid and semiarid areas, due to the lack of proper management of renewable natural ‎resources, not only the proper utilization of water and soil resources is not done, but also ‎water becomes a natural disaster, and every year, floods cause many human and financial losses. One of the integrated methods of flood control operations is flood spreading. This method improves the status of utilization of water and soil resources, plant cover, and artificial ‎recharge of groundwater. ‎Sediments that are carried with the flood, deposit in flood spreading region and may change the physical and chemical properties of soil over time. The most serious danger which threatens the flood spreading networks and artificial recharge ‎schemes is the reduction of the infiltration of soil due to sedimentation. ‎‎The most important factor affecting the performance of flood spreading systems is the ‎amount of input sediment into the spreading canals, its depositing on the surface and ‎accumulation in the depth of soil, which can change the physical and chemical properties of the soil. In this regard, current research was conducted to investigate the role of input sediments into flood ‎spreading field, determine the penetration depth of sediments and the spatial pattern of ‎physical and chemical changes in soil. ‎Materials and MethodsKashmar flood spreading station is located in 17 km east of Kashmar, in the longitude of 58° 38’ to 58° 40’ of the east and latitude of 35° 15’ to 35° 39’ of the north. This research was conducted in the first Phase of Kashmar flood spreading. ‎ In this research, the first five channels of dewatering were divided into three study networks ‎‎(outset, middle, and end), and the upstream of the spreading flood arena was considered as the control sample. In each grid, three points were selected as repeat tests and soil profiles were drilled with a depth ‎of 1 m. In each soil profile, the soil samples from 050 and 50100 cm depths were provided. At the test site, soil infiltration was determined using double rings. After transferring soil samples to the lab, the soil texture (clay, silt and sand percentages) was determined by the hydrometer method. In the laboratory, the value of the chemical parameters of the soil, including soil acidity (PH), electrical conductivity (EC), bicarbonate (HCO3ˉ), sulfate (SO42), chlorine (Cl), potassium (K+), and sodium (Na+) were measured. The effects of flood spreading on the physical and chemical ‎properties of soil in spreading filed were investigated with the factorial experiment in a completely randomized ‎block design. ‎ResultsThe results of the analysis of variance showed that there was a significant difference between the ‎soil infiltration in channels 1 to 5 and the control arena at the probability level of 1%.  However, there was no significant difference (p=%5) in soil infiltration in the start, middle, ‎and end sections of the channels. ‎ In channels 1 to 5 and in the control arena, there was no significant difference (p=%5) in the amount of sand, silt, and clay. Flood spreading increased the amount of the clay in the depths of the channels compared to the control area. The Analysis of the variance showed all chemical properties of the soil. Except potassium, there was a significant difference (p=%1) between the dewatering channel and the control field. ‎The amount of the variables did not change in the second depth compared to the control arena. The interaction ‎effect between the depth and channel was not significant at 5% probability level. ‎ Thus, flood spreading did not change the chemical characteristics of soil in depth.Discussion and ConclusionThe rate of the soil infiltration in spreading channel reduced 4.3 times of soil infiltration in the control arena. The least infiltration was observed in channels 1 and 2 due to the proximity of these channels to the source of flood and deposition of more suspended load on the surface‎ of the soil. Because the suspended load of floods increased the clay particles and reduced the macro porosity, it decreased the soil infiltration. Flood spreading caused an increase of 1.5% in the soil acidity of the channels compared to the ‎control arena. ‎ A 30% reduction in electrical conductivity was observed in the first two and third channels, compared to the control arena‎. The amount of HCO3, Cl, SO42, and Na+ reduced in the first, second, and third channels but increased in the fourth and fifth channels. The amount of potassium in all channels decreased compared to the control samples but this decrease ‎was not significant‎. In general, flood spreading in Kashmar site caused the diminution of soil infiltration, which had a negative effect on flood spreading system. Therefore, it is recommended that water spreading channels are plowed every year to increase soil ‎permeability. ‎