| Weihe river is the largest tributary of the yellow river and plays an important role in the harness and development of yellow river.Wei river basin is the relatively water deficient area,especially the Guanzhong region,where water shortage was complex and serious.There are several types of the factors leading to water shortage,such as resource,engineering,management and pollution.How agricultural water use directly diverted from Wei river in the Guanzhong irrigation area affects basic ecological flow draws the national and social attention.Therefore,Baojixia irrigation area,as the largest irrigation area at the Guanzhong section of Wei river,was chosen as a research subject to study the impact of water diversion of the Baojixia irrigation area on the basic ecological flow of Wei river.The simulation experiment of the canal water and sediment transport in the irrigation area was conducted.In addition,the tested data about water and sediment in the area was collected.Then the following targets was realized: to set up the canal water and sediment transport model,to study the impact of variation in water utilization structure in the irrigation area on the basic ecological flow of Wei river,to discuss the impact of agricultural water conservation of integrated canal water and sediment dispatching to the basic ecological flow of Wei river,and to provide agricultural water saving measures and joint scheduling mode of water resources employed to maintain basic ecological flow of Weihe river.The main results were as follows:(1)Relationship between incoming water and sediment of Weihe river and water requirement and water diversion in Baojixia irrigation district.Long-term data of incoming water in Weihe river was analyzed.It showed that in space,it is not easiest for Qianhe reach into Weihe river to guarantee ecological base flow at Guanzhong section of Weihe river;in time,lack of water concentrated in dry season,especially December,January and February in the river course of Weihe river.Average multi-year incoming water and water diversion were 10.91×108m3and 4.58×108m3,respectively.It showed that average annual water diversion was less than 50% of incoming water.However,average multi-year water diversion of headworks accounted for 91.82%?90.57%?84.41% of incoming water from Weihe,respectively,in Baojixia irrigation district in December,January and February,whichmeans that average multi-year water diversion was nearly 90% of incoming water during the winter irrigation period.It was very difficult to satisfy the standard 4 to 6 4 ~ 6 m3/s of ecological base flow for Linjiacun and Weijiabu reach,which was given by the nation,yellow river conservancy commission and Weihe administration.Therefore,water use regulation in Baojixia irrigation district should be crucial to guarantee the base flow of Weihe river during the period of winter irrigation and spring irrigation.Crop water requirements in Baojixia irrigation district were between 2.56×108m3and7.55×108 m3 under current situations,the average value of the water requirements was2.71×108 m3.The total number of water division for irrigation and sediment transportation and power generation were between 5.23×108m3and 13.2×108m3,which was much higher than the number of crop water requirements.It was an important problem that how to regulate water for irrigation and sediment transport to meet the environmental bsse flow.(2)Research on effect of canal sediment transport on reducing pollution and increasing fertility and congruent of sediment transport in the irrigation district of the middle and lower reaches of the Yellow River.The sediment transport experiments of polluted rivers were designed in the condition of concrete canal based on available sediment carrying capacity observation of earth canal of Weihuiqu canal as a consequence of pollution of Weihe river.It aimed at studying water and sediment transport in the polluted condition and providing support of theory and technology for setting up canal water-saving regulation model used to guarantee ecological base flow of Weihe river.Results showed that sediment distribution in the canal was in accordance with the laws of sparseness in the upper part and denseness in the lower part along the way.Pollutant concentration with flow transport showed non-significant downward trend in 40 m-long tested canal.The impact of canal sediment content on chemical oxygen demand(COD),total nitrogen(TN)was significant,the experimental result illustrated that the sediment grain reduced COD and increased TN in the water,which means that the sediment grain had an degradable effect on COD and nitrogen element was completely dissolved in the water,namely owing effect of reducing pollution and increasing fertility.Sediment carrying capacity in the irrigation district was in accordance with sediment transport in the irrigation district of the lower reaches of the Yellow River.Sediment carrying capacity formula of earth canal and concrete canal and recovery saturation coefficient of sediment transport were given in the irrigation district,and canal hydraulic property was studied.They provided suggestions for setting up the impact of water and sediment scheduling in the irrigation district on the basic ecological flow of Wei river.(3)Scheduling model of water and sediment in the Baojixia irrigation area was constructed.One-dimensional constant non-uniform water and sediment schedulingmodel in the irrigation area was developed by our research group.The compute module of water and sediment scheduling model about the impact of Baojixia irrigation area on the basic ecological flow of Weihe river was given through the debug and calculation in combination with the scheduling model on basis of the above water and sediment transport experiment.Furthermore,its water level,flow,sediment discharge and canal scouring and silting was validated.The validation showed that maximum difference between calculated and observed water depth was 0.04 m,and relative error was 2%.Total siltation and average siltation for canal were 1.6×103m3and 0.016 m3 per linear meter,perceptively.And calculated total siltation was 2.6×103 m3,which was greater than observed siltation.In addition,the tendency of calculated grading curve was generally in accordance with that of observed curve.This means that constructed model could be used to calculate the impact of water and sediment scheduling in the irrigation area on the basic ecological flow of Weihe river.(4)Impact of agricultural water use in the Baojixia irrigation area on the basic ecological flow of Weihe river.Water in the Baojixia irrigation area was diverted from the main stream of Weihe river,and hence how much water was used in the area had an direct impact on the basic ecological flow of Weihe river.Water use in the area consisted of agricultural water use and canal water use for sediment and pollution discharge.Results of the mathematical operation showed that discharge capacity on average reduced by 30% when the sedimentation increased by 1.0 m in the main canal.The main canal in the irrigation area generally lost the discharge capacity when cumulative sedimentation arrived at 3.0 m.36 million m3 water was needed to wash against 1 m sedimentary canal through the model calculation.(5)The scheduling mode of water resource in the irrigation area was given to maintain the base flow.Irrigation water demand was 317 million m3 and 501 million on the plateau of the Baojixia irrigation area in the normal and dry years.Water resource need to be reasonably allocated and the ecological base flow in Linjiacun be maintained in 4 m3/s.Based on this,surface water was dispatched by 283 million m3 and ground water by 33 million m3 to guarantee agricultural water demand in the normal year.For the dry year,surface water was460 million m3 and ground water was 41 million m3 to maintain agricultural production.Irrigation water demand under the plateau of the Baojixia irrigation area was 229 million m3 and 363 million m3.In the same way,water resource was properly allocated,ecological base flow at Weijiabu was guaranteed in 6 m3/s and sediment concentration of diverted water was not greater than 8%.On this base,water diversion from the river was 280 million m3 and ground water was exploited by 70 million m3 to maintain irrigation water demand in thenormal,and for the dry year,water from the river was 280 million m3 and ground water 82 million m3 to maintain agricultural production. |
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