| Aiming at the huge areas of a cone of depression due to overexploitation in the downstream of irrigated area diverting Yellow River of the flood plain of china, Linqing City of Shandong Province was selected as the pilot project area with a feature of highly permeable formation and the Yellow River water of a low turbidity introduced by farmland ditch. Moreover, the MAR projects named open canal-underground perforated pipe-shaft was used to alleviate the problem of a cone of depression. The water infiltrated from the perforated pipe could recharge the groundwater while the canal infiltration and irrigation return water also recharge the groundwater. The MAR project could prevent the physical clogging through the three anti clogging measures of pre-filtration device, slope pipe and shaft with other advantages of gravity driving without extra energy, no land occupation,managed recharge and water logging control.The study on general layout, project type, seepage theory, parameter design and benefit analysis were conducted with field survey, theory analysis and calculation. The study results are as follows:(1) The field surveys of geophysical prospecting, ground investigation, double-ring permeability test and the laboratory test such as water quality test and soil test had been conducted. In addition, the local hydro-geological data showed that the zone of aeration of the pilot project area is silt with high permeability and there is no continuous aquitard, moreover,the foreign water, Yellow River water, is stable and high quality. In general, the stratum and the water are appropriate for recharge.(2) According to the MAR guidelines of Australia, the entry level risk assessment included viability and degree of difficulty had been carried out to estimate if the efficient and ecological MAR project is viable in the pilot while two degree indicators of unsaturated zone permeability and construction technique were added based on the project characteristics. The assessment result shows that the project is suitable for the area generally except the slope failure because of the silty soil. However, it can be avoided by optimizing construction scheme.(3) The MAR type of open canal- underground perforated pipe-shaft was proposed according to the project area characteristics and ancient tunnel-well in Huantai County as well as the present material and filter technology. The water level of the open canal is the dynamic of seepage and filtration without extra energy; pre-filter is used to remove major suspended solids against clogging in the perforated pipe and soil surrounding the pipe; the underground perforated pipe has the functions of percolation, sediment and water transport; the shaft can accept and deposit reminder silt, in addition, the desilting can be conducted through sand-flushing and back washing.(4) The technical scheme was designed, the calculation formulas of different seepage stage were determined and the recharge result was calculated according to the soil hydrodynamics, hydraulics and groundwater dynamics. The pilot project area covers 6.7hm2 with three installations, and parameters for one installation are as follows: the base area of the filter tank is 4m2; the buried depth of pipe, inner diameter, length, gradient, aperture ratio and the distance of the filter pipes are 4m, 30 cm, 200 m, 1/500, 25% and 90 m respectively; the depth of the shaft is 10 m. The calculated recharge result showed that the recharge amount of groundwater added by the MAR project is 15498m3 with a length of 7 days with raising average groundwater level of 2m and extending the recharge range of 800 m which account for 18.6% of the whole recharge amount.(5) The national economic benefit and financial evaluation of the project combined with irrigation engineering of water saving were analyzed in the condition of plantation structure domitated by cash crops. It is showed that the ratio of benefit to cost are both more than 1. In addition, the project can replenish groundwater, repair the depression cone, etc. In a word, the MAR project has the obvious economic, ecological and social benefits.In conclusion, the MAR project named open canal-underground perforated pipe-shaft is feasible in technology with obvious benefits. It can alleviate the conflict between supply and demand of irrigation water to some extent through restoring a cone of depression, ensure the healthy development of irrigation water and ecological environment and afford the technical support for agriculture development even the whole social-economic development in well-canal combined irrigated area of Shandong Province. |
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