Research On Endowment Characteristics And Sustainable Exploitation And Utilization Of Groundwater Resources In Deyang City

The groundwater endowment characteristic is the material basis and prerequisite for development and utilization.Deyang is a city which is based on groundwater as the main source of water-supply in southwest China.Water conservation function is the main feature in mountain area with fault-fold structure,groundwater level declining and water quality deterioration occur in some places of the plain area,and shortage of groundwater resource is main problem in red beds area.Obvious different groundwater endowment characteristics are showed and various groundwater exploration conditions and social-economic development level are presented in different regions.The contradiction between the increasing demand for water and the shortage of water resources,water pollution and deterioration of water environment is very prominent,especially after the “5.12” earthquake.It is urgent to study comprehensively the regional differences of endowment characteristics of groundwater resources and its relationship with the sustainable development and utilization of groundwater resourcesHydrogeological survey and data collection,hydrogeological investigation,statistical analysis,groundwater resources evaluation,groundwater dynamics analysis,hydrogeochemical method,groundwater quality evaluation,dynamic monitoring are adopted to analyse the hydrogeological characteristics of Deyang city systematically,also to summarize the regional differences of the water resources endowment and the relationship between the main functions of the groundwater and the development and utilization of the groundwater.Evaluation indicators system of groundwater sustainable exploitation and utilization,with differences in endowment of groundwater resources,was built on the basis of sustainable development theory,systematic theory and attribute theory of groundwater.GIS spatial analysis function,improved analytic hierarchy process,entropy method,dimensional analysis method,comprehensive index method are comprehensively used to process the indicator data and carry out the evaluation classification and division,and then carried out case studies.The research of this thesis has some innovative achievements in enriching the groundwater resources sustainability theory,method and applied technology system.The main achievements are as follows:（1）The rainfall in faulted-folded mountainous area in west and red beds areas in east of Deyang is more than plain area.The precipitation is concentrated from April to October,accounting for more than 90% of the whole year.Faulted-folded mountainous area,with alpine-gorge landscape,is the birthplace of the Mianyuan River and the Shiting River.The strata are exposed from Sinian system（Z）to Jurassic（J）,with intense folds and faults.Rivers and diversion canals intersect in Plain area,creating erosion and deposit landscape.Quaternary are exposed and geologic structure is simple in the area.The red beds area is mainly composed of the gullies and the canals,and Jurassic（J）and Cretaceous（K）are exposed and slight folds and few faults are distributed.（2）Faulted-folded mountain area can be divided into 5 types of aquifer,in which fissure-karst aquifers（T₂t、T₂j+l、P₂c、P₂l、P₁m+q、C₁d、C₁y、D₃tn、Zbdn）have the best water abundance.The accumulation of groundwater is obviously controlled by water storage structure.As a whole,it has regional hydrodynamic linkage,showing marginal recharge,internal pressure bearing,and excretion to deep valley.It is complicated by interference of internal uplift.The variation of water quantity in bedrock fissure water and carbonate fractured karst cave is greatly affected by rainfall.Interstratol water in clastic rocks is less affected by rainfall.And groundwater is characterized mainly by HCO₃-Ca·Mg type,and which change from HCO₃-Ca·Mg type to HCO₃·SO₄-Ca or HCO₃·SO₄-Ca·Mg type in part of the Miyuan and Shiting rivers where industrial and mining enterprises are distributed.Plain area can be divided into 4 types of aquifers.The upper aquifer composed of Q₃^fgl+al muddy gravel layer and Q₄ ^al,Q₄^al+pl gravel layer have the best water enrichment.Groundwater receives atmospheric precipitation and surface water supplies.The water abundance is obviously controlled by the genetic types and geomorphic characteristics of Quaternary sediments and forms abundant groundwater resources.Rainfall infiltration,Irrigation infiltration and Abstraction groundwater regime types are included,and groundwater level declines seriously in well field for concentrated water supply.As dominated types,HCO₃-Ca、HCO₃-Ca·Mg、HCO₃·SO₄-Ca、HCO₃·SO₄-Ca·Mg types account for 92.41% of the water samples.The distribution area of HCO₃·SO₄-Ca and HCO₃·SO₄-Ca·Mg types increased by 597.83km² compared with 1990 s.Red areas can be divided into 3 types of aquifers.fissure-pore groundwater aquifers（K₁g、K₁q、K₁b、K₁c、J₃p）are the most widely distributed.Groundwater is mainly concentrated in " the areas suitable for small diameter borehole " on both sides of the valley.Aquifers generally do not have regional hydrodynamic links,mainly in local supply,near discharge,and minor cycles.Groundwater samples is characterized mainly by HCO₃-Ca type.HCO₃·SO₄-Ca type increased by 316.1km² compared with 1990 s,while HCO₃·Cl-Ca type increased by 29km².There are similar distributions between hydrogeological unit and landform unite and tectonic unit in Deyang city.Hydrogeological boundary is the main controlling factor of groundwater endowment divisions,and groundwater development prospect is secondary factor.On the basis of the main controlling factor and secondary factor,groundwater resources endowment divisions in Deyang City are identified,including fissure-karst groundwater resources endowment division in faulted-folded mountain area（I）,pore groundwater resources endowment division in the plain area（II）,and fissure-pore groundwater resources endowment division in the Red bed area（III）.The recharge modulus and exploitable modulus of aquifers are 7.35-21.6×10⁴ m³km^-2a^-1 and 0.65-18.20×10⁴ m³km^-2a^-1 in endowment division（I）,which have the strongest water yield among all the aquifers with better water quality.The recharge modulus,storage modulus,and exploitable modulus are 12.9-76.9×10⁴ m³km^-2a^-1,25.0-405.0×10⁴ m³km^-2,and 0.65-18.20×10⁴ m³km^-2a^-1 in endowment division（II）,respectively.Holocene alluvial sand and gravel aquifer has the strongest water yield among all the aquifers.Three groundwater quality grades are evaluated for the 80 samples,of which 51.25% are good quality,42.5% are poor quality,and 6.25% are very poor.The recharge modulus are 5.1-21.7×10⁴ m³km^-2a^-1 in endowment division（III）,the storage modulus and exploitable modulus are 0.68-15.5×10⁴ m³km^-2 and 2.16-7.14×10⁴ m³km^-2a^-1 within the areas suitable for small diameter borehole.Thus the exploitable groundwater resources are poor.64% of the 50 samples are good quality,34% are poor quality.（4）Endowment division（I）,with abundant Karst groundwater resources,simple chemical types,and good water quality,plays a role in ecological protection and water conservation.Exploitation condition is not good for industrial and agricultural water supply,and springs are the main source of water supply.Endowment division（II）,with abundant pore groundwater resources,plays a role in large scale water supply.Compatibility between groundwater development and social-economic development and environment should be emphasized because of over exploitation,groundwater level declining and water quality deterioration in some places of the plain area.The exploitable groundwater resources are poor and the purpose of groundwater abstraction is to meet the basic drinking water for people and livestock in endowment division（III）.（5）On the basis of groundwater endowment characteristics analysis,the relationship between the differences of endowment divisions and groundwater development is translated into quantitative indicators.AHP method is applied to build evaluation indicators system of groundwater sustainable exploitation and utilization after the groundwater attribute classification of indicators.The indicators system consists of 3 hierarchies,which are object hierarchy,constrain hierarchy and indicator category hierarchy,and 6 types of indicators,which are regulation and recovery,availability,development and utilization status,guarantee capacity,ecological and environmental indicators.Different groundwater endowment characteristics are shown in different areas of Deyang city.The indicators system are divided into 3 sub-systems which are sub-system suitable for pore groundwater in Quaternary unconsolidated rock,sub-system suitable for fissure and karst groundwater,sub-system suitable for fissure-pore groundwater in the Red bed area.（6）In the process of treating data,dimension of the selected indicators is unified as "L" or dimensionless by dimensional analysis,and the indicators are highly comparable.Rasterization and union-dividing analysis methods are applied to extracting data.Direct assignment is used to standardize the indicator data,and grading standards are identified according to the related standards and research results.The single indicator value is limited to [0,1] by standardization.The subjective weight is modified by the difference degree of objective weight coefficient,and the weight coefficient is obtained well.It is a more reasonable method to determine weight.The grading of sustainable capacity is classified into very poor sustainability[0,0.2],poor sustainability(0.2,0.4],middle sustainability(0.4,0.6] good sustainability(0.6,0.8],excellent sustainability(0.8,1.0].（7）Groundwater resources Sustainable exploitation and utilization evaluation are carried out with the case study of the plain area of Deyang city,mountain area in Shifang county,and red bed area in Jingyang district.The selection of indicators takes into account the actual situation of the study area and the degree of difficulty in gaining indicators.The evaluation results show that there are four degrees of sustainable capacity in the plain area of Deyang city,including very poor sustainability（27.7km²）,poor sustainability（285.9km²）,middle sustainability（656.2km²）,good sustainability（940.2km²）,accounting for 1.5%、15.0%、34.4%、49.2% of whole plain area,respectively.There are four degrees of sustainable capacity in mountain area in Shifang county,including very poor sustainability（93.7km²）,poor sustainability（143.9km²）,middle sustainability（211.5km²）,good sustainability（50.0km²）,accounting for 18.8%、28.8%、42.4%、10.0% of whole area,respectively.There are three degrees of sustainable capacity in red bed area in Jingyang district,including poor sustainability（133.4km²）,middle sustainability（126.4km²）,good sustainability（5.3km²）,accounting for 50.3%、47.7%、2.0% of whole area,respectively.The evaluation results are in good agreement with the reality.