Background Water damage is the main disaster that threatens the safety of pipelines in mountain. Runoff scouring of pipeline construction scope is an important manifestation of water damage. Although some researches have been carried out on prevention and control of slope runoff, however, problems of interception and drainage of construction scope of pipeline in mountain still often occurs, such as inadequate protection, excessive protection or unreasonable protection. Therefore, it is necessary to conduct a systematic study on design standards and protective measures system of slope runoff of construction scope in mountainous areas.

Methods We selected highway, railway, municipal, water and soil conservation, oil and gas pipeline industry design standards and specifications for comparative analysis on interception and drainage of slope runoff. Then we selected 4 typical along-laying slopes and 4 typical cross-laying slopes of the mountain pipeline from Puning, Guangdong, Beilun, Zhejiang, Cangxi, Sichuan, Tongnan, and Congqing in the southern humid area to carry out hydrologic calculation and discuss the design essentials of interception and drainage system.

Results 1) Different design standards of interception and drainage are formulated according to different engineering grades and protection objects in highway, railway, municipal, water and soil conservation. 2)Simplified rational formula shall be adopted for hydrologic calculation of slope runoff, and the calculation accuracy can be improved by using local rainstorm atlas parameters.3) According to the calculation, the slope runoff of pipeline section with equal length in cross-laying slope is 8-10 times that of along-laying slope in southern humid area. For along-laying slope, the interval flow is 0.01-0.02 m³/s with an interval of 25-30 m, and the intercepting ditches or water blocking stems can be used to intercept runoff. The durability requirements for such structures are relatively low. For cross-laying slope, the interval flow is 0.12-0.20 m³/s with an interval of 30 m, and the interval flow is 0.19-0.34 m³/s with an interval of 50m. The intercepting ditches shall be set at the inner side of cross-laying construction scope, and the runoff shall be introduced to the downhill side based on microtopography. Such structures shall be considered to have certain durability and should adopt masonry, concrete and other structural forms. 4)In arid and semi dry areas in North China, fish scale pits, horizontal ditches and other land consolidation methods can be used to regulate slope runoff.

Conclusions It is suggested that the design recurrence interval of flood for along-laying slope should be 3-5 years, that of cross-laying slope should be 20-30 years for pipelines with DN 800 and above, 15-20 years for pipelines with DN 200-DN 800, and 10-15 years for pipelines less than DN 200. The interception and drainage system on construction scope should be formulated according to the characteristics of cross-laying slope and along-laying slope in mountainous areas.This study can provide reference for the design and construction of hydraulic protection and water and soil conservation of pipeline projects in mountainous areas.