The flow moving within subterraneous karst conduits is termed conduit flow. Conduit flow is a special geomorphologic and hydrological phenomenon in karst area. It is a typical indication of dual water-bearing medium and binary structure with extreme specialty and complexity. Being of a rapid response to the heavy rain and with the close relationship to slope flow and fracture flow, conduit flow, mainly as the turbulent flow, always shows the great variety during the different seasons and in distinct karst land mass. The ratio of maximum runoff of conduit flow to minimum one reaches from 10:1 to 1000:1. Thus, underground water hydrodynamics is not suitable for the research of conduit flow. Based on the systemic theory, trace mark technique as a main monitory method is being applied to study the karst hydrological processes, relationship and connection within the underground river system, ratio of the runoff between different conduit flows, contaminants diffusion in karst water and more and more other concerned problems at present time.

Houzhai River drainage basin in Puding, Guizhou province is a large scale test field in the main and broad karst area in southern part of China, where conduit flow is a general reserve and drainage system for underground water. It is a model of mountain karst river basin, with the area of 81 km2, and with two underground reservoirs in its upper stream, which are the ideal sites to draw water for pulse test. Based on the great deal of field investigation and indoor research works during 70s and 80s, pulse tests have been done four times there during 1988 to 1991 in wet and dry seasons. According to the relevant response curves of pulse wave, the connection in this underground river system has been revealed directly. It also shows that water level at each observation site changes from 10 to 1800 mm, with the larger variation in upper stream and at karst windows than in lower reaches and at each exit along subterraneous rivers. By analyzing the lasting time of initial reaction in response curve, the average flow velocity in conduit system is determined within 200-800 m/h, with the less change from flood to dry season, and it is higher in principal conduits and in upper stream area. Meanwhile, the response of water level is always faster than that of gross hardness or electrical conductivity, the later represents the hydrochemistry situation in conduit flow, which shows the difference between wave velocity and flow velocity exactly. Furthermore, while there is full of water in conduit, the difference is even sharper. Then, by measuring the rate of water discharge during pulse tests, reliable divided discharge ratio in each hydrological conduit of sunken system has been got. Combined with detailed field survey in this area, the river system has been exposed finally.