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Research on Eco-Environmental Water Requirement of Tarim Mainstream Watershed

Author: HuShunJun
Tutor: KangShaoZhong;SongYuDong
School: Northwest University of Science and Technology
Course: Agricultural Soil and Water Engineering
Keywords: ecological-environmental water requirement phreatic water evaporation ecological system conformity Tarim mainstream watershed
CLC: X171
Type: PhD thesis
Year: 2007
Downloads: 1018
Quote: 8
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Abstract


Tarim River is honored of“Mother River”by the people living in southern Xinjiang. Because large ecological water use was deprived by agricultural water use in source flow area and the upstream and midstream of main river, the 320-kilometer watercourse of lower reaches of Tarim River was cut off for a long period, Taitema lake was dried, groundwater table was decreased substantially, natural vegetation has become degraded and the catastrophic weather phenomenon of floating dust, sand-dust storm are brought about frequently. In order to provide scientific bases for ecology-oriented optimal allocation of water resources in Tarim basin, the Tarim mainstream watershed was selected as research area to conduct systematical research on ecological-environmental water requirement in this dissertation. The main research contents and conclusions are showed as follows:(1) Date of phreatic evaporation from bare soil in the Tarim mainstream watershed are collected, the law of phreatic evaporation is analyzed, the analytic solution for calculating the limited rate of phreatic evaporation is deduced, and calculation models of phreatic evaporation from bare soil with more reasonable structure are established. Phreatic evaporation in growing Tamarix, Populus euphratica and Phragmites communis is measured by integration of soil moisture content profile and phreatic depth, and models for calculating phreatic evaporation from vegetated lands are therefore established, and the feasibility for calculating eco-environmental water requirement by calculating phreatic evaporation is finally analyzed. The research results show that the relationship between phreatic evaporation power coefficient and content percentage of clay particle and silt of different soil texture is exponential, vegetation conversion coefficient decreases with the increase of phreatic water depth, and the value of eco-environmental water requirement estimated by calculating phreatic evaporation is less.(2) Evapotranspiration of Tamarix, Populus euphratica and Phragmites communis in different soil moisture condition is measured by field experiment, and models for calculating plant evapotranspiration are established. The research results show that the relationship between the ratio of evapotranspiration to evaporation from water surface and the soil moisture content of root zone not only accords with Logistic curve but also relates with evaporation from water surface.(3) By using mathematical statistics method, comprehensively considering the relationship among phreatic water depth, soil moisture content, soil salt content and plant growth, depth of main root zone, and height of soil capillary rise, the reasonable ecology depth of phreatic water in the Tarim mainstream watershed is determined and value for Tamarix is 2.20~4.62m,Euphrica 2.53~3.43m and Phragmites communis 1.92~2.73m.(4) Supposing that the relationship between intensity of phreatic evaporation and phreatic water depth is linear, deduction of the analytic solution of phreatic water depth on the banks of lower reaches of Tarim River is carried out under long-term water conveyance condition. The new conception of groundwater recharge volume is put forward and the preliminarily estimated value is 21.05×108m3 from Daxihaizi to Taitema lake in the lower reaches of Tarim river.(5) Based on the relationship among phreatic water depth, soil water content in the main root zone,the ratio of natural vegetation evapotranspiration to evaporation from water surface, and the effective principle of soil water for plant growing, this dissertation divides preliminarily the ecological-environmental water requirement norm of natural vegetation into three grades with the given quantitative grading standard i.e.“fundamental existence water requirement”,“the maximum suitable ecological-environmental water requirement”and“the minimum suitable ecological -environmental water requirement”. At the same time, the ecological-environmental water requirement norm of natural vegetation in different target grades and the ecological-environmental water requirement of different target grades in different river stretches are calculated by introducing the plant cover degree as the area weight of the plant of patch distribution.(6) The reduced coefficient of annual water surface evaporation of shangyou reservoir and Tamen town are 0.58~0.59 and 0.50~0.54 respectively. The ecological water requirement of annual water surface evaporation is about 5.76×108~14.17×108m3 in the Tarim mainstream watershed.(7) On the basis of principle of water-sand balance, semi-empirical and semi-academic formula for calculating water requirement for sediment transport is put forward. The saline drainage coefficient is redefined and the method for calculating leaching norm is modified and perfected. Based on the generalization and evaluation of the calculation methods of river-channel ecological-environmental water requirement and by comprehensively considering the feature, the main ecological-environmental function and the data situation of the Tarim mainstream watershed, the water requirement for sediment transport, minimum ecological water requirement for maintaining the existence of aquatic organism in river system, environmental water requirement for improvement of water quality and the environmental water requirement for preventing and curing alkalization of farmland were calculated.(8) By means of conformity of the ecological-environmental water requirement and analysis of water balance of river reaches in the Tarim mainstream watershed, the ecological-environmental water requirement of different target grades in different river stretches and the yearly runoff of hydrometric sections are calculated based on hydrologic cycle process. Under the condition of fully supplying the total water requirement for sediment transport, the ecological-environment water requirement of natural vegetation, the environmental water requirement for preventing and curing alkalization of farmland, the minimum ecological water requirement of maintaining the existence of aquatic lives in river system and the environmental water requirement for preventing pollution can be all fully supplied in Tarim mainstream watershed.

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CLC: > Environmental science, safety science > The basic theory for the Environment and Science > Environmental Biology > Ecosystems and pollution ecology
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