Low Impact Development construction of peak cluster depression based on regulation of epikarst zone

Most of the bare karst areas environments with the widest distribution in southern China have peak cluster depression landforms. With high incidence of many environmental problems such as rocky desertification, flood, water shortage, and water pollution, the karst environment there is proved to be very fragile. For the bare karst environment, it has a very developed subterranean river drainage networks, causing most of the water resources to enter the aquifer, and then flow and discharge rapidly through the underground karst conduits. For a long time, as a karst living environment, the lack of water and soil resources have become the main cause of environmental degradation.The introduction of the concept of Low Impact Development (LID) is necessary and timely in the karst peak-cluster depression area, based the rich research and practice in southern China. It is believed to be effective for promoting the utilization of water resources, reducing human disturbance, and covering the other environmental problems, such as rocky desertification and risk of underground river pollution. The LID methods based on the regulation of the epikarst zone and sinkholes are mainly suitable for guiding the development of karst land in dolines and depressions. It is realized by solving the questions of how to plan the land use and to design the rural infrastructure according to the special hydrogeological conditions and epikarst hydrological process. The concept and technology of LID in view of urban facilities will give guidance for the construction of a holistic environmental remediation project in a rural area, including water resources storage, pollutant treatment, and land restoration for rocky desertification. It is very helpful to promote rural revitalization in the remote and fragile ecological environment area of karst rocky mountains. Karst dolines naturally have topographic and hydrogeological conditions that promote rapid rainfall infiltration. Controlled by monsoon climate, the karst environment is characterized by distinct rainy season and dry season. Due to the lack of soil cover, storm water forms various types of runoff on the rocky slope, which flows into the underground river eventually through epikarst zone and sinkholes. The epikarst zone with a high degree of karstification has high hydraulic conductivity and regulation and storage function with a large number of small caves. It is the main water storage space on the slope and forms the epikarst spring. The bottom of the depression is flat with continuous soil cover. The flood is discharged by the sinkhole, but sometimes the groundwater inversely enters the karst depression through the sinkhole, resulting in waterlogging. Karst depressions are widely used as living space and agricultural planting. According to its terrains, development practice and disturbance intensity, the land of karst doline can be divided into three kinds of sensitive areas, and they are, (1) sloping farmland with risk of soil erosion, (2) epikarst springs for drinking water source with risk of pollution, and (3) the sinkholes with risk of contaminant input. The LID model would try to achieve five management goals in the three sensitive areas.(1) The goal of LID in the sloping farmland is to minimize water consumption by crop irrigation and to protect precious and thin soil from erosion, which technically can be achieved by requiring a filtering system such as building terraced fields, interception basin and straw mulching, so as to regulate soil moisture and slope flood runoff. (2) The management goals of the sensitive areas of epikarst springs are the utilization of rainfall-runoff resources and the ensurence of drinking water safety, which technically can be achieved by implementing rainwater harvesting projects and setting up water source protection area. (3) Contaminant interception and absorption facilities, such as buffer zone and sedimentation and filtration ditch, should be built in the sensitive area of sinkhole for achieving the goal of stopping contaminants entering groundwater. The LID model for peak cluster, or “LID based on epikarst”, which is characterized by rainfall -runoff management in the epikarst zone, has been explored and summarized in the karst rocky desertification region of South China. The model requires reserving the water resources in the woodland area at the top of the peak in the process of development planning and utilization of karst depression, for enhancing the recharge by infiltration through epikarst zone. In the intensive utilization of land at the bottom of karst dolines, the buffer zone would be reserved for controlling flood discharge by sinkholes, and a low elevation green belt is set with filled karst grooves for promoting natural infiltration and purification. In the transition zone between “peak” and “doline”, the scope and boundary conditions of water confluence at epikarst spring should be clearly defined, and the boundary of the water source protection zone should be determined. At the same time, it is necessary to increase the utilization of rainwater to supplement the water shortage of ecosystems and living. Although LID model based on epikarst is raised from the rocky desertification control in southern China, it could be possibly extend to the karst areas in other regions such as Southeast Asia, where peak-cluster is also well developed.