Interaction Of Surface Water And Groundwater In Ordos Cretaceous Basin

Ordos basin contains a wealth of natural resources including coal, petroleum and natural gas and it is one of the most important bases for China's energy and heavy chemical industries in the 21st century. Unfortunately because of arid and semi-arid climate and rare precipitation and strong evapotranspiration, there is a severe shortage of water resources in Ordos basin that has hampered industrial development and eco-environmental improvement and adversely affected people's livelihood. Ordos Cretaceous basin is an independent large scale groundwater basin in the middle and west of Ordos Basin where the large amount of groundwater resources is the major supply water sources for local energy exploration and energy base construction. In the basin, the interaction between surface water and groundwater is not understood due to the frequent and complex interaction. Therefore, the study of the interaction of surface water and groundwater is significant in practice and theory for the build of the water circulation and the development of water resource in Ordos Cretaceous Basin.Environmental isotope can trace water cycle effectively because isotope can sign and dating water circulation and chemical component of water is the production of water evolvement. Consequently it will be used to study the interaction of surface water and groundwater that using hydrogeochemistry combines with isotope. The main topic of the thesis is to study the interaction between surface water and groundwater through investigating the characteristics of stable isotopic and chemical component of surface water and groundwater on both sides of river. The main achievements of this paper are as follows:1. The interaction between rivers and groundwater in the south area of Ordos cretaceous basinThe Loess Plateau river network is well developed in the south area of Ordos cretaceous basin and the river valleys are deep, which disclosed the cretaceous bedrock aquifer that groundwater level is higher than the rivers level. By the impact of topography, geological structure and litho-paleogeography conditions, TDS of rivers and groundwater is widely high and decrease along the river flows.δ¹⁸O andδD of rivers is at the between of precipitation and groundwater, and its change in trends is consistent with groundwater along the river flows, except for individual reaches. Combining with the characteristics of geochemical distribution and the isotopic composition in the rivers and the groundwater on the both sides of the valleys, that is easily to be known rivers in the south area are recharged by precipitation and groundwater which is disclosed by rivers, and in upper reaches the rivers is mainly recharged by the precipitation, and in the middle and lower river reaches the rivers is mainly recharged by the groundwater.In the Malian River, TDS and ratio of C?l-/ (Cl-+HCO3-) is higher, however, ratio of Na⁺/ (Na⁺+Ca2+) is no law. Along the river flows, except for individual water samples, TDS of river decrease and consistent with Huanhe groundwater at the both sides of river. Major ions of river have the same characteristics. The slope ofδ¹⁸O andδD (4.05) in the river is lower than that of local meteoric line (7) and global meteoric line (8). Andδ¹⁸O andδD in the river are between of precipitation and of groundwater. In the river source area, the ratios of the stable isotope is different with the Huanhe groundwater, and along the river flows, except the middle reach, river water has the same change trends with the Huanhe groundwater. Based on the characteristics of geochemical distribution and the isotopic composition of the Malianhe River and the groundwater on the both sides of the valleys, and combining with analysis of the hydrogeology condition of the Malianhe River valleys, it is obviously that different ways of interaction between river and groundwater is different in different reaches of Malianhe River. In Malianhe River. source area, it is mainly recharged by the precipitation. the upper reach is discharge area of Huanhe aquifer, where the river is mainly recharged by the groundwater of humane aquifer. in the middle reach, the river is still recharged by the groundwater of Huanhe aquifer, but the hydraulic connection between the river and the groundwater is not closely like the upper reach. In the lower reach there is not hydraulic connection between the river and the groundwater of Huanhe aquifer, where the river is mainly recharged by Cenozoic aquifer.In the Luohe River, TDS, ratios of Na⁺/ (Na⁺+Ca²⁺) and of Cl^-/ (Cl^-+HCO₃^-) is higher, TDS of river decrease and consistent with Huanhe groundwater and Luohe groundwater at the both sides of river, however, river water change rate is smaller. The slope ofδ¹⁸O andδD (5.72) in the river is lower than that of local meteoric line (7) and global meteoric line (8). Andδ¹⁸O andδD in the river are between of precipitation and of groundwater. In the river source area, the ratios of the stable isotope are consistent with the Huanhe groundwater. Above Danbazhen, the ratios in the river increase, and below Danbazhen, the ratios decrease. Based on the characteristics of geochemical distribution and the isotopic composition of the Luohe River and the groundwater on the both sides of the valleys, and combining with analysis of the hydrogeology condition of the Luohe River valleys, it is known that Luohe River is mainly recharged by the humane aquifer. In the upper reaches of Danbazhen function of groundwater recharge of humane aquifer is weak except in source area. In the lower reach of Danbazhen river is recharged by Luohe aquifer.2. The interaction between rivers and groundwater in the north area of Ordos cretaceous basinIn the north of basin, the water system doesn't develop, the river network is sparse, the rivers are short, and the riverbed is wide and shallow, with small flow as seasonal river. At the low-lying area, most of the lakes, which are formed by the inland rivers'convergence, are saline soda lake because of intensive evaporation. The upper river valleys in the north area of basin dissect the aquifer in the cretaceous bedrock aquifer, which groundwater level is high. The groundwater with the characters of low TDS and fresh water developing is similar to river which TDS is also low. In different groundwater systems, the difference of hydrochemistry variation characteristics along the river is big. But the hydrochemistry of source area of the river and groundwater is same.δ18 and δD in most of rivers are higher than the local rain and groundwater, the variation characteristics along river flows are different in various reaches, but the isotopic composition in river source area is consistent with in groundwater at both sides of river. Based on the characteristics of geochemical distribution and the isotopic composition of the river and the groundwater on the both sides of the valleys, we got that the origin of rivers in the north area is groundwater, and the rivers are recharged by groundwater, and there are surface runoff mixed along river flows.In the Dusitu River, TDS is more than 1g/l, ratios of Cl-/ (Cl-+HCO3-) and Na⁺/ (Na⁺+Ca²⁺) are both high. The trends of them in the reach from DST3 to DST6 are different from in groundwater on the both sides of river, but in the other reaches the trends are same. TDS in river is increasing river flows, and is higher than in groundwater. The change trends of main ions in Dusitu River are similar to TDS. The slope ofδ¹⁸O andδD (3.9) in the river is lower than that of local meteoric line (5.88) and global meteoric line (8). And the isotope ratios (δ18 andδD) in river are higher than in local precipitation. The variation characteristics of isotope ratios (δ¹⁸O andδD) alone river flows is consistent with in groundwater at both sides of the valleys. Based on the characteristics of geochemical distribution and the isotopic composition of the Dusitu River and the groundwater on the both sides of the valleys, and combining with analysis of the hydrogeology condition of the Dusitu River valleys, we got the interaction between rivers and groundwater as follow: in the reach from NB3上to DST3, the river gets recharge from precipitation and groundwater;In the reach from DST3 to DST6, river gets recharge from groundwater;In the reach from DST6 toDST7, groundwater gets recharge from river.In the Wuding River, TDS is more than 1g/l, ratios of Cl-/ (Cl-+HCO3-) and Na⁺/ (Na⁺+Ca²⁺) are both high. TDS in river decrease alone river flows, which is consistent with in groundwater at the both sides of the valleys. The slope ofδ¹⁸O andδD (5.72) in the river is lower than that of local meteoric line (5.88) and global meteoric line (8).δ18 andδD in rivers are between the groundwater in Salawusu aquifer and rain. The trend of river from upper to lower reaches are basically identical with groundwater, both of them have three times peak-valley alternative variation, and variation of river lags behind groundwater, and the variationδD alone runoff is more similar. Based on the characteristics of geochemical distribution and the isotopic composition of the Wuding River and the groundwater on the both sides of the valleys, and combining with analysis of the hydrogeology condition of the Wuding River valleys, it is be known: in the upper reach, the river is recharged by groundwater of the humane aquifer; in the middle reach, river is recharged by groundwater of Salawusu aquifer; and in the lower reach, river is recharged by precipitation and groundwater of Salawusu aquifer.In the Molin River, TDS, ratios of Na⁺/ (Na⁺+Ca²⁺) and of C?l-/ (Cl-+HCO3-) is higher, and consistent with groundwater. TDS, Na⁺, Cl- and SO42-of river which decrease along river flows have adverse trend with groundwater at both sides of river.δ¹⁸O andδD in the river are between of precipitation and of groundwater. The ratios of the stable isotope have good relevance with groundwater at both sides of river and are in contrast with groundwater. Above water sample ML2, the ratios in the river increase, and below water sample ML2, the ratios decrease. Based on the characteristics of geochemical distribution and the isotopic composition of the Molin River and the groundwater on the both sides of the valleys, and combining with analysis of the hydrogeology condition of the Molin River valleys, it is known the interaction between rivers and groundwater as follow: in the reach from ML1 to ML2, river is recharged by groundwater, and in the reach from ML2 to ML4, river is recharged by precipitation and groundwater.3. The interaction between lakes and groundwater in the north area of Ordos cretaceous basinThis thesis chose Dakebo and Yanhaizi of the Molinhe-Yanhaizi groundwater system as typical lakes. Through analysis on the characteristics of geochemical distribution and the isotopic composition of the lakes in the north area and using indication function of ¹⁸O to water cycle, we established mathematical-physical model to estimate the transformed capacity between lakes and groundwater.The analysis show that the lakes in the north area of Ordos cretaceous basin is recharged by surface runoff and groundwater in their collection area. Near the watershed, the proportion of surface runoff recharge to the lakes is high in the total, but near the discharge area, the proportion of groundwater to the lakes is high. The recharge to Dakebo lake from surface runoff is 468×10⁴m³, which accounts for 43% of the total water supply, and the recharge from groundwater is 613×10⁴m³, which accounts for 57% of the total water supply. The recharge to Yanhaizi lake from surface runoff is 1007×10⁴m³, which accounts for 37% of the total water supply, and the recharge from groundwater is 1742×10⁴m³, which accounts for 63% of the total water supply.