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Study On Film-Covering Bed Furrow Irrigation And Its Water-Saving Mechanism

Posted on:2006-08-31Degree:DoctorType:Dissertation
Country:ChinaCandidate:X Y ZhangFull Text:PDF
GTID:1103360155455860Subject:Agricultural Soil and Water Engineering
Abstract/Summary:PDF Full Text Request
Compared with the pressurized irrigation systems, for example, sprinkle irrigation and micro-irrigation, etc., the surface irrigation has advantage of less invest, lower operating cost and convenient management, etc. and well-managed surface systems can achieve irrigation application efficiencies close to those of pressurized systems. At the present, more than 95% of the irrigation field of the whole world and 98% of our China is irrigated by surface irrigation. But bad-managed surface systems have more vertical seepage, lower uniformity and irrigation efficiency. These seriously affect its water application efficiency. Furrow irrigation is the vital method of surface irrigation. It can't damage the soil texture and result in soil harden, can decrease expiration loss, and is usable as cultivated crop of wide row spacing. Its infiltration method belongs to two-dimensional infiltration and has complex influencing factors. Its management and operation is more complex than the border irrigation method. So it has important meaning to agricultural water-saving and yield increasing of studying, improving and perfecting furrow irrigation technique, improving water application efficiency and irrigation uniformity, decreasing water requirement. Based on the experiment study of influencing factors of two-dimensional infiltration of furrow irrigation, this thesis brings forward and system studies film-covering bed furrow irrigation (FBFI) technique. It has some improvement and consequent by the study of infiltration characteristic, surface flow moving characteristic, water-saving effectiveness and irrigation uniformity, system optimum and practice on the field. 1. The infiltration experiment was conducted to study the effects of such factors as water depth, bottom width, bottom hydraulic conductivity of irrigation furrows, and initial soil moisture content on two-dimension infiltration in furrow irrigation. The results revealed that reducing the water depth and bottom hydraulic conductibility of irrigation furrows, and increasing initial soil moisture content were beneficial to increasing horizontally lateral infiltration and concurrently reducing vertical infiltration but their bottom width only affected lateral infiltration other than vertical infiltration; when the width decreased, the vertical infiltration decreased. Of these affecting factors, the bottom hydraulic conductivity showed the strongest influence on infiltration. When the irrigation quota was 45 mm, the depth of the vertical water infiltration decreased by 41% at the conductivity of zero compared with that in bare ground irrigation thereby remarkably changing the shape of infiltration body to low and smooth parabola shape in furrow irrigation. It can decrease seepage and increase lateral infiltration. Based on this, it brings forward FBFI technique. This technique can decrease the vertical infiltration of the bottom of irrigation furrow and surface roughness of furrow, increase lateral infiltration and advance velocity of surface flow in the furrow by covering un-pervious film on the bottom of irrigation furrow. It provides an effective approach and feasible thinking for realizing higher irrigation uniformity, less vertical seepage loss, surface irrigation of little water requirement which has higher irrigation efficiency and is a new feasibility and reasonable water-saving surface irrigation technique. 2. The infiltration experiment was conducted to study the effects of such factors as water depth, slope factor of irrigation furrow, and wetted perimeter on two-dimension infiltration characteristics of FBFI. The infiltration rule and characteristic of FBFI are proved elementally. Of these affecting factors, the slope factor and wetted perimeter of irrigation furrow showed the evidently influence on infiltration, but water depth in the irrigation furrow didn't show. On the condition of the same planned water requirement, infiltration body of FBFI is low and smooth parabola shape, deep seepage is notably decreased, distributing of soil water content is uniformity, soil water content in the designed soil moisture layer is higher than conventional furrow irrigation (CFI). 3. The field experiment was conducted to study the effects of such factors as furrow length, inflow discharge, and water requirement on surface flow moving characteristics of CFI and FBFI. The rules of surface flow moving of FBFI are gained. The results revealed that the advance and recession process of surface flow of CFI and FBFI have the same rules of inflow discharge and irrigation time are greater, and advance distance and velocity are greater. But on the same condition, the advance distance of FBFI is greater about 50% than CFI, and advance velocity is about thrice of CFI, and water depth in the irrigation furrow reaches stabilization quickly. Recession time is longer and rough twice of CFI. This leads that distributing of storing water infiltration time along the furrow length of FBFI is more uniformity than CFI and irrigation uniformity is improved remarkably. It found that the lateral infiltration cumulative underground 10 ~ 40 cm layer of FBFI is greater evidently than CFI, soil water content higher, infiltration distance lengthier, vertical infiltration less by measuring the distributing of soil water content. 4. On the base of these researchers, the mathematical models are developed to simulate infiltration and surface flow moving of FBFI by the use of the modified Richards'equation and Kinematic-wave model. Combined with initial condition, boundary condition and relative parameter, numerical solution is obtained by Galerkin finite element method. Thefounded model is steadier and reasonable and well agreed with the data obtained from field irrigation experiment by validating. It establishes the base for more studying infiltration characteristic and surface flow moving characteristic, irrigation technical parameter optimum, system management and design, etc. It studies the effects of such factors as roughness factor and soil hydraulic conductivity of irrigation furrow on surface flow moving in furrow irrigation. While roughness factor and soil hydraulic conductivity of irrigation furrow are deceased, the advance time is shorter, advance velocity and irrigation uniformity are increased. 5. It analyzed and evaluated the water-saving effectiveness and irrigation uniformity of FBFI on the base of the experiment results. On the same condition, the water-saving efficiency of FBFI is more than 35% and water requirement is less, water-saving efficiency is greater. Soil water content distributing of FBFI along the furrow length is better than CFI and irrigation uniformity of FBFI is more than 0.85 whether in the irrigation furrow or on the irrigation furrow ridge. 6. The FBFI system is optimized depending on the founded Kinematic-wave model and using evaluating index of irrigation quality, water application efficiency, storage efficiency, and irrigation uniformity, as target. It studies the effects of such irrigation technical parameters as furrow length, inflow discharge, and irrigation time on surface flow moving and irrigation quality on the condition of FBFI and gains the optimum combination of irrigation technical parameters of FBFI. It gains that the effect of irrigation time on irrigation quality is most, inflow discharge is next, and furrow length is least. The optimum combination is that inflow discharge is 1.0 l/s, furrow length 70 m, irrigation time 110 min. The effect of the interaction of 3 irrigation parameters isn't evidence and most is the combination of inflow discharge and irrigation time, next is the combination of inflow discharge and furrow length, last is the combination of irrigation time and furrow length. 7. The field experiment is conducted to more explore the infiltration characteristic, surface flow moving, irrigation quality and the effect on the corn of FBFI. The results revealed that irrigation uniformity of FBFI is higher and lateral infiltration is better than the CFI on the condition of little water requirement irrigation. The corn yield and irrigation application efficiency of FBFI is greater than that of CFI. The FBFI is an effective little water requirement surface irrigation technique.
Keywords/Search Tags:surface irrigation, FBFI, two-dimensional infiltration, surface flow moving, irrigation uniformity
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