| This research was carried out based on the major Twelfth Five-year prospecting project of China Geological Survey-Groundwater exploration and demonstration of water-supply safety in the area of serious shortage of water resource in Wandashan, Heilongjiang province(Item NO.:12120113103000). Based on analysis of regional geologic setting and hydrogeological conditions, pumping test, groundwater monitoring, analysis and testing and other related work with the help of geophysical prospecting and logging data were cariied out, to further analyze and summarize systematically the hydrogeological conditions of the area next to the reservoir, identify the distribution characteristics of well-watered fissure zones, obtain the hydrogeological parameters, calculate the recharge-discharge quantity between surface water flow field with groundwater flow field, and to discuss compensation balance and mechanism of conversion between surface water and fissure groundwater.(1) Geologic setting and hydrogeological conditionsIt is concluded by comprehensive analysis that geomorphic units which the area next to the reservoir belongs to is the valley plain of Woken river and its both sides’low mountains and hills, the Quaternary sedimentary thickness of the valley plain is generally about 10m, the biggest thickness can reach more than 20m and has obvious dual structure. The sandstone and conglomerate of Houshigou group, Cretaceous underlies the Quaternary strata, whose sedimentary thickness is generally about 40-60m, and unconformable contact with underlying Chengzihe group, the deposition of the thick-layer conglomerate and wide distribution of the coal line are the main bases of the stratigraphic division.The formation and evolution of the basin are divided into two phases through a comprehensive analysis of stratigraphic sequence, the evolution, of sedimentary, tectonic features, developmental history of basin, namely the development phase and reform phase, the development phase includes five developmental stages and the reform phase includes six stages:the development phase of the basin has gone through the following five periods, which are the initial crack, expansion, the largest expansion, contraction and atrophy from bottom up; The basin reformation mainly refers to a series of geological events influenced by crustal movement after the deposition of Houshigou group, mainly includes three phases and six stages:the first phase is small folds of Houshigou group, late Cretaceous; the second phase means that in the late Paleogene-Neogene, complex anticline formed, the axis of fold of Houshigou group formed tensile fracture or tension cracks; the third period is the reform period since Neogene, and then formed glutenite of the bottom of Houshigou group and sandstone fracture zone of the upper Chengzihe group after two times of tensional rift expansion and compression uplift. The fracture generally develops in five directions:EW, NE, NW, NNE, and NNW. The generation time of fracture is generally as follows:NS and EW are earlier, followed by NE, and NEE, NWW are the latest; The interpretation data of geophysical prospecting shows that there exits 10 fractured zones in the valley of Woken river, generally cut through the glutenite of Houshigou group, late Cretaceous; The analysis of vertical zonation of the fault zone combining hydrogeological drilling, logging data shows that faults, fissure zones and cave passages develop intensely with the depth of 10-50m depth, and there exit faults and fissure zones in the depth of 40-60m,120-130m,130-150m.The paper systematically summarizes the groundwater types of the area next to the reservoir, zones as water abundance in detail, summaries the law of recharge-runoff-discharge of groundwater. The groundwater types of the area next to the reservoir mainly include three types of groundwater:water in porous media of the Quaternary aquifers, water in Cretaceous sandstone fissures and water in Neogene basalts voids-fractures. The Cretaceous sandstone fissure water is divided into weathering fissure water in the hilly area and tectonic fissure water underlying on the bottom of the river valley of Woken river. Quaternary loose rock pore water mainly distribute in the river valley of Woken river and its tributaries, Quaternary unconsolidated rocks sedimentary thickness in the section of Qitaihe City Taoshan - Beixing farm twenty-four team is big, Aquifer lithology is mainly the coarse sand, gravel and pebble. Particle size of sand and gravel are big, Good connectivity Groundwater runoff unobstructed, Hydrogeology is stronger, Single well water inflow can reach 100-1000m3/d; Woken river valley plain river tributaries and the upper reaches of the river valley plain, Quaternary sedimentary thickness is relatively smaller, aquifers are mainly the coarse sand, water content is relatively weak, single well water inflow Generally less than 100m3/d. The composition of Aquifer are Holocene loose coarse sand, pebble gravel, silty clay gravel and coarse sand silty clay, thickness changes great, generally 1-2m, groundwater depth generally 4-5m. Neogene basalts are dense block, aphanitic structure, With vesicular or almond -shaped structure, Weathering fissure and Columnar joints are Development, water rich but without water, Excellent permeability, The flow of springs is small, generally less than 10m3/d. Tectonic fissure water occurs in the lower entrance Daikin Shahe River valley downstream Woken. The zone of high water storage is mainly located in the fissue zones of the Houshigou and Chengzihe sandstone and gravel sandstone. NW-trending extensional fault and tectonic pressure twisted band edge after the first pressing of the tensile fracture, rock fracturing was serious. With the development of fissures, connectivity was enhanced, groundwater runoff unobstructed. The Single well water inflow can reach 1000-3000m3/d, Water chemistry type is mainly HCO3-Ca and HC03-Ca·Mg, with good water quality. Weathering fissure water mainly refers to Cretaceous sandstone weathering fissure water, the discharge of the springs being 10-100m3/d.Atmospheric precipitation is the main source of Groundwater recharge. The secondary source of recharge is mountain lateral recharge (Lateral mountain runoff and Valley undercurrent), irrigation supply (surface water irrigation and groundwater irrigation), recharge from river. Cretaceous fractured groundwater flow in pores, fissures and dissolved voids along fracture zones. Accept Pre-Quaternary bedrock weathering fissure water Quaternary pore water supply, by Fracture zone、Fissures and caves formed by water guide channel and dissolved gap flow to lying areas downstream.(2) Calculation parameters selection and groundwater resource evaluationUsing the equations for steady state single well pumping test, non-steady state single well pumping test and group well pumping test, the permeability coefficient of Quaternary aquifers was calculated, with an average of 22.5m/d. The Cretaceous sandstone structure fissure water permeability coefficient was calculated to have an average of 71.75m/d, Hydraulic conductivity coefficient of glutenite fracture zone of Cretaceous bottom Houshigou is 1833 m2/d, According to empirical parameters, precipitation infiltration coefficient of Valley plains is 0.1, precipitation infiltration coefficient of Hills calculate partition is 0.12, Aquifer thickness in Main valley is 25m, Tributary is 5m, Close the Reservoir within the 120km2, Groundwater recharge to the Cretaceous -based computing partition recharge. The total amount of recharge is 2098.10×104m3/a, namely 5.74×104m3/d. the amount of atmospheric precipitation recharge is 562.44×104m3/a, take up 26.80% of the total amount of recharge; Lateral groundwater recharge for runoff is 1024.44x104m3/a, take up 48.97% of the total amount of recharge; Recharge from river is 508.23×104m3/a, take up 24.22% of the total amount of recharge. Recharge from calculated partition of Quaternary loose rock pore water is 837.60×104m3/a, take up 39.92% of the total amount of recharge; Recharge from calculated partition of Cretaceous sandstone fissure water is 1260.50×104m3/a, take up 60.07% of the total amount of recharge. Evaporation close the Reservoir is 1206.2×104 m3/a, Lateral groundwater runoff excretion is 1030.43×104 m3/a, Labor exploitation is 9.51×104 m3/a, Groundwater total excretion close to the reservoir is 2246.14×104m3/a. Use interference well group method for calculating the amount of groundwater exploitation of resources and the evaluation of the study area is 5.00×104m3/d. Using both the average values, the amount of water resources was calculated to be 5.14×104m3/d. Drop coefficient is calculated using the analogy method, when Ground water level dropped to 40m, the extraction was 14.94×104 m3/d; When Ground water level dropped to 50m,the extraction was 18.30x 104 m3/d.(3) Mechanisms of compensation balance between surface water and groundwater in fractured zonesBased on years of rainfall data, one hydrological year groundwater monitoring data and reservoir monitoring data, detailed calculation of the monthly suppley and excretion of surface water field systems and groundwater systems, the natural state and compensation equilibrium state of surface water and groundwater extraction and mechanismswere studied. The natural environment in the "underground water field" is still the original natural state, has not been interfered by human, Water features are excellent natural area. Due to under reservoir intercepted, Fissure water wet period is saturated, Taoshan reservoir groundwater play a role in regulation and storage, not only strengthen vertical and lateral strength of the surface water for groundwater recharge, And whether or Wet year, flat year or dry year, can effectively alleviate the water sources of groundwater level decline, play an important role in Sustaining exploitation of water sources. Natural state, affected by the ground elevation, new water sources of the groundwater level is always higher than the reservoir water level, annual groundwater recharge is from Taoshan reservoir. In extreme drought years,water levels of Reservoir is stable capacity of 171.57m, When the pump dynamic water level falls below this level, start to accept supplies from reservoir water level, at this time, from the upstream of lateral fissure water still is the main recharge;A sharp decline in the water level, the Quaternary water is drained, and the upstream weathered water supply capacity is diminished. So the difference between the reservoir water level and dynamic water level will increase. Since the first layer fracture zone water conducting capability is extremely strong, supply capacity of source reservoir increased gradually. Until the water level drop of about 50m, the net reserves of the first layer fracture zone will be drained. When water level of water head site is reduced to less than 50m, the reservoir supplement will decline, and the reservoir begins to use net reserves and recharge in the lower part, until the reservoir is dry and lose the recharge capacity.(4)Groundwater numerical Simulation and PredictionBased on a depth analysis of the geology and hydrogeology in Heilongjiang Wanda serious dry land emergency water source The area next to the reservoir, Qitaihe Woken River Valley Taoshan reservoir upstream, this study establishes numerical simulation of groundwater flow model The area next to the reservoir, multilayer aquifer (banded) structure on the use of GMS. This model simulates Cretaceous sandstone structural fissure water and the Quaternary loose rock pore water. Then we identify and validate the model using the measured data, and the result is excellent which indicates the flow model established achieves a high accuracy. Therefore, the model we establish can be used as a groundwater flow forecasting model. Through recognition and validation, we propose four kinds of different options for the future long-term and emergency exploitation, and predict groundwater resource trends.From a long-term sustainable use of groundwater in the area, the daily abstraction quantity no more than 52,000m3 is appropriate. Under exploitation conditions, the depth of the water table decline is small; the region drawdown remained within 4.0m; and the demonstration area and the surrounding environment will not cause adverse effects. If we mine groundwater for continuous five years, the maximum drawdown is 3.64m, and the water level elevation is at 177.35m around; for continuous ten years, the maximum drawdown is 3.26m, and the water level elevation is at 176.35m around; for continuous five years, the maximum drawdown is 3.77m, and the water level elevation is at 176.30m around. So normal exploitation is guaranteed, the water sources can address the needs of domestic water5.5-6×104m3/d.From the point of emergency exploitation, in the case of extremely dry year which the precipitation P=97% guaranteed rate, if emergency exploitation maintain a year, the reasonable exploitation amount is 18.2×104m3/d on the conditions that groundwater level drop to 50m(near the bottom of the first layer of fractured zone). Nine months later the reservoirs will recharge groundwater 8.5×104m3/d, and twelve months later will recharge 12.2×104m3/d. Nine-month cumulative recharge from reservoirs to groundwater is for 1213.6×104m3, and twelve-month is for 1930×104m3. If emergency exploitation is 20x104 m3/d, six months later the reservoirs will recharge groundwater 6.69x104m3/d, and nine months later will be 13.62×104m3/d. Six-month cumulative recharge from reservoirs to groundwater is for 806.6×104m3, and nine-month is for 1930×104m3.As a result, the reservoirs will dry up, and lose the ability to supply. Therefore, the reasonable time is not more than four months, and the emergency exploitation time is up to eight months. If emergency exploitation is 15×104 m3/d, nine months later the reservoirs will recharge groundwater 6.60×104m3/d, and twelve months later will be 9.1×104m3/d. Nine-month cumulative recharge from reservoirs to groundwater is for 833.1×104m3/d, and twelve-month is for 1751.9×104m3/d. So the reasonable exploitation time is not more than eight months, and the emergency exploitation time is up to one year. If we mine groundwater as above solutions, there are a lot of impacts on local groundwater resources and Taoshan reservoir storage capacity, but the emergency ability will greatly improve. Because the groundwater is fissure water of rigid rock, water-rich zone is not easy to be destroyed. The water yield and level in water sources can still restore after the peak water supply in the spring of the second year. It is recommended that the water be exploited only in the emergency time, and the emergency extraction amount be 18.2×104m3/d, and the time be less than 12 months. |
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