بررسی تاثیر توپوگرافی بر کمبود رطوبت خاک در دامنه های حوضه های آبخیز با استفاده از TOPMODEL

نویسندگان

چکیده

مقدار کمبود رطوبت خاک یک پارامتر کلیدی در محاسبات نفوذ، تخمین منطقه اشباع دامنه و به دنبال آن تخمین جریان سطحی و زیر‌سطحی براساس دو مکانیسم هورتونی و دانی بلاک است. مدل هیدرولوژیکی TOPMODEL قابلیت اندازه‌گیری میزان کمبود رطوبت خاک تا حالت اشباع در هر نقطه از دامنه را دارد. پاسخ هیدرولوژیکی دامنه‌های حوضه آبخیز به شکل پلان (همگرا، موازی و واگرا) و انحنای دامنه (محدب، صاف و مقعر) بستگی دارد. در این پژوهش یک مدل TOPMODEL، به طوری که بتواند تأثیر هندسه و توپوگرافی دامنه‌ها را در محاسبات کمبود رطوبت دامنه‌ها در دامنه‌های مرکب در نظر بگیرد، ارائه شده است. نتایج پژوهش نشان داد، چنانچه دامنه مستطیلی صاف به‌عنوان مبنا در نظر گرفته شود، هندسه دامنه همگرای محدب بیشترین تاثیر و دامنه موازی مقعر، کمترین تأثیر را بر کمبود رطوبت خاک در بین دامنه‌های مرکب دارند. علاوه بر این، همگرایی بیش از واگرایی و تحدب بیش از تقعر بر تغییرات کمبود رطوبت خاک اثرگذار است.

کلیدواژه‌ها


عنوان مقاله [English]

Investigation on effect of topography on soil moisture deficit of catchments’ hillslopes using TOPMODEL

نویسندگان [English]

  • Touraj Sabzevari
  • Shabnam Noroozpour
چکیده [English]

Soil moisture deficit (SMD) is a key factor in evaluation of infiltration, estimation of saturated zones and surface and subsurface flow according to Hortonian and Dunne-Black mechanisms. The parameter SMD in each point of a watershed can be estimated by TOPMODEL. The hydrologic response of hillslopes depends on their plan shapes (convergent, parallel, and divergent) and profile curvatures (convex, straight, and concave). In this research, geometry of the complex hillslopes was concerned as new parameters in TOPMODEL to extend the equations governing the model. Also, the effects of complex hillslopes geometry on SMD and subsurface flow were studied. The TOPMODEL introduced by Beven and Kirkby (1979), provides a simple approach to parameterize the effects of topography on the distribution of subsurface moisture and runoff generation, and has been added into models of catchment hydrology and forest ecology. It has been widely applied to a variety of water resource theories, developments and applications [e.g., Beven and Wood, 1983; Beven et al., 1984; Wood et al., 1990].TOPMODEL has been used to soil moisture mapping, geochemical fluxes, subsurface flow and erosion. Examples of TOPMODEL applications in a range of locations may be found in the following works: Beven et al. (1984); Hornberger et al. (1985); Beven (1986); Wood et al. (1988); Robson et al. (1992); and Quinn and Beven (1993). Beven and Kirkby (1979) were among the first to work on TOPMODEL subject. They employed topographic index methods to predict variable contributing areas. The topographic index, , where a is the area drained per unit contour length and is the slope of the ground surface at the location, has been found by Beven and Kirkby to compare favorably with observed patterns of surface saturation. In this research the equations relevant to TOPMODEL were studied and developed considering geometry of hillslopes. Fortunately, TOPMODEL was capable to consider plan shape and curvature of complex hillslopes. We gave an account of saturation index sigma introduced by Troch et al. (2002) which is computable for the nine complex hillslopes and in close relation to geometry of hillslopes. The mode of the saturation index equation bore much resemblance to that of SMD in TOPMODEL. In this article, the relationship between these indexes was scrutinized and an equation was presented obtaining SMD from sigma. An equation regarding convergence, divergence, convexity, and concavity was introduced to calculate SMD for complex hillslopes.
Curvature influences on the velocity of water flow into soil and decreases travel time. Plan shapes of the hillslopes effects on flow width as well as drainage area. SMD in TOPMODEL is depended on the drainage area and slope of the hillslopes. At the first step, SMD was computed in two simple cases (regardless of geometry) and in the complex case along the hillslope to compare the results. Accordingly, the most changes corresponded to the convergent convex, and the least were of the concave parallel hillslope. The convergent hillslopes affected the SMD, 20% more than the divergent ones, on average. Also, the convex hillslopes reacted more relatively to the concave ones. At the second pace, the effects of convergence, divergence, convexity, and concavity on SMD were studied more accurately.
The main goals of this research were: Development of Topmodel equations to consider geometry of complex hillslopes in the nature; Studying the effects of complex hillslopes geometry on soil moisture deficit; Computing subsurface flow of complex hillslopes using COMPLEX TOPMODEL.
According to the results, the convex convergent hillslopes had the greatest variation in SMD, while the parallel concave hillslopes had the least. Convergent hillslopes showed more reactions to geometry comparing to the divergent hillslopes, and the same fact holds for the convex hillslopes relative to the concave ones. The more rainfall recharged rate, the faster saturation occurred along with less SMD. An increase in SMD happened when SA enlarged as long as the other conditions of hillslope were constant. TOPMODEL having vast applications in estimation of flows under sub-catchments (corroborated by the previous studies), could yield better results in the complex cases. Precise computation of SMD has great importance in the rainfall-runoff models. In this research the subsurface flow equations were developed for complex hillslopes, and an equation was presented by which the subsurface flow profile and the average discharge in each hillslope could be computed based on the sigma index.

کلیدواژه‌ها [English]

  • TOPMODEL
  • Complex hillslope
  • Soil moisture
  • SMD