Spatial distribution of underground river streams and water resource in the Chongqing Municipality

Karst rocks in the Chongqing Municipality in southwestern China covers about 3.0×10~4km~2,accounting for approximately 36.49% of the total area of Chongqing.The 1/(200 000) hydrogeological map of Chongqing and the relevant reports show that there are approximately 380 underground streams with a total length of about(1 898.43km,) with a total mean discharge of more than 144.20m~3/s and water resources of more than 4.547×10~9m~3/a.The underground streams,in general,exist mostly in the southeast and northeast of Chongqing.The distribution of the underground rivers is consistent with the occurrence of the carbonate rocks in Chongqing.Three indicators,i.e.,the development density,runoff modulus and multi-year average precipitation,are used to judge distribution of the underground streams in Chongqing.The coefficient of development density of the underground streams varies between 12.25m/km~2 and 263.37m/km~2,and the coefficient of runoff modulus of the underground streams,between 0.10L/(s·km~2) and 22.89L/(s·km~2).It appears that variation exists from region to region.The high development zones occur in the west and southeast of Chongqing.The high runoff modulus zones concentrate in the northeast,southeast and west of Chongqing.In Chongqing,it is also found that the high-density zone of underground streams is not necessarily the high runoff modulus zone,and the high rainfall zone is not necessarily the high runoff modulus zone.