Main Participants: CHEN Zuyu, YU Shu, YIN Penghai, WANG Lin, YUE Fan, HAO Jianwei, LI Yingzhe, SUN Ping, SONG Jianzheng, CHEN Yongsheng

Check dams are one of the effective engineering structures for soil and water conservation in the Loess Plateau of China,which experience much more serious failures and greater risks than conventional embankment dams. Led by Chen Zuyu, Academician of Chinese Academy of Sciences (CAS), the research team completed numerous national-level research projects and proposed a series of innovative technologies based on relevant theories in hydraulic structures and modern information technologies. The original achievements have been made regarding the risk evolution mechanism and prevention & control technologies for check dam breaches, aiming to tackle the safety challenges faced by check dams during the flood season.

·   Flood analysis modelling for check dams breaches;

·   Breach risk analysis of clustered check dams;

·   Developing check dams breaches risk prevention and control technologies, such as flexible spillways and pre-stressed concrete cylinder pipe conveyance;

·   Developing a breach risk monitoring, prediction, early warning, prevention and control  platform for clustered check dams.

·   A flood analysis model for check dams breaches coupling water and soil parameters has been proposed, i.e. the progressive flow-induced soil erosion, has been put forward. A model for the lateral expansion of the breach and a hyperbolic erosion model for compacted loess have been developed. An erosion testing cylinder has been developed to accurately obtain the critical shear stress threshold and erosion rate of typical loess.

·   A precise breach risk analysis method for the complicated cascade/parallel clustered check dams has been proposed. A calculation procedure for clustered check dam consecutive failures has been set up by figuring out the logical relationship among check dams through the "family tree" diagram similar to human generational relations. And an evaluation method for the loss from check dam breaches has been developed.

·   A flexible spillway technology for check dams has been pioneeringly proposed. Geotextile bags have been made using COMPET composite geotextiles, which are filled with local compacted loess and applied in the construction of  spillway and stilling basins. The feasibility of the flexible spillway technology for check dams have been validated through scaled model tests and field prototype tests.

·   A pre-stressed concrete cylinder pipe (PCCP) technology for check dams has been developed. The PCCP technology has been developed considering that the discharge structures of check dams need to withstand high levels of internal water and earth pressure load and they shall have good impermeability and durability.

·   A risk monitoring, early warning, prevention and control technology based on information technology for clustered check dams has been put forward. The technologies of multi-level coordinated operation and management as well as digital monitoring, supervision for check dam systems have been proposed along with the technologies for failure risk early warning, prevention and control.

·   Suggestions and comments on the construction of high-standard check dams have been provided. The research team has submitted a report titled "Suggestions on Improvement of Flood Risk Prevention and Control Capabilities and High-Quality Construction of Check Dams in the Yellow River Basin" to the CPC Central Committee and the State Council, which has been recognized by state leaders with written instructions and comments.

The flood analysis model for check dams breaches has been included as Appendix A in the updated Technical Specification of Check Dams, and has been widely applied in dam reinforcement in the Loess Plateau. The flexible spillway technology for check dams has been included in the "List of Mature and Applicable Scientific and Technological Achievements in Water Field for Promotion and Application in 2020" by the Ministry of Water Resources; and has been applied successfully to the Baicaowa check dam and the Shijiagou check dam in Yulin, Shaanxi Province, the Sanlian dam in Yan'an, Shaanxi Province, and the Xi'aogou No. 8 check dam in Linfen, Shanxi Province. The PCCP technology for check dams has been included in the updated Technical Specification of Check Dams as one of the recommended discharge structures of check dams for water transfer, and has been applied successfully to the Wangyayao check dam and the Tiaozigou check dam in Yan'an, Shaanxi Province.

Fig.1 Application of the clustered dam breach risk analysis method to the Xiwuselang Gully clustered check dams in Erdos, Inner Mongolia

Fig.2 Stepped flexible spillway technology for check dams - Baicaowa check dam demonstration project in Yulin City, Shaanxi Province. (a) Layout of the site, and (b) detailed illustrations of the longitudinal and the cross section views.

Fig.3 Application of the failure risk monitoring, early warning, prevention and control technology to the Xi'aogou check dam system in Linfen City, Shanxi Province

Fig.4 The report led by Prof. Chen Zuyu, Academician, submitting to the CPC Central Committee and the State Council