Development and distribution of karst subterranean streams in Chongqing,China

Karst groundwater is an important strategic resources and life-support system for sustainable development in southwest China.There is 3.0×104 km2 karst area and 380 karst subterranean streams(SS)in Chongqing municipality as important groundwater resources.This study summarizes the controlling factors of development and distribution of SS from the opinion of lithologic characters,geological structure and landform in Chongqing according to the historical 1∶200,000 hydrogeological reports with abundant field works from 2007 to 2009.Results show that the number of SS is the most abundant in pure and thick carbonate strata and the developing degree of SS is well.While,the number of SS is little and the developing degree is weak in other impure carbonate rock,due to the lower calcite content and karst processes rate.A new founding is that the formation and distribution of SS is controlled by the lineament structure in Chongqing.As a whole,the SS distributes mostly in the Eastern Sichuan fold belt,Southeastern Sichuan fall-fold belt and Mt.Daba arc-shaped fault-fold belt of Chongqing.The bearing of trend of SS in Mt.Daba arc-shaped faultfold belt in northeastern Chongqing is NW-SE direction because of the control of the NW trend lineament structure.Due to the influence of the NE and NNW trend lineament structure,the bearing of trend of SS in Southeastern Sichuan fall-fold belt in southeastern Chongqing is NE-SW direction.The SS mainly locates in the core part of a series of anticlines in Eastern Sichuan fold belt in the main districts of Chongqing City and central area of Chongqing municipality,which is the carbonate rock area,and its trends is along the anticline extension direction(NE direction).According to the structure features and groundwater movement features of SS,it is divided into the following three types:afflux-flow type,distributary-flow type and parallel conduit-flow type.The afflux-flow type SS largely distributes in the syncline areas,wide-spaced shallow-dip anticline areas and ridge-trough valley areas.The distributary-flow type SS mainly locates in the anticline areas and syncline chapada areas,and the parallel conduit-flow type SS in the appressed fold areas which is the areas of soluble rock alternating with non-soluble rock.