Observation and analysis of water temperature and ice cover in the middle route of South-to-North Water Diversion Project in 2014-2022 winter

The middle route of South-to-North Water Diversion Project has been in operation for 8 winters since its full operation in December 2014, and the water conveyance flow is controlled to 30%-50% of the design flow during the ice period in order to prevent the ice jam disaster, which seriously restricts the water conveyance benefits of the project. Therefore, the channel water temperature and ice cover have been one of the key issues in winter water conveyance. Field measurement data shows that (T)Winter water conveyance flow generally increased year by year, and the end canal section remained relatively stable, the flow rate of Gangtou sluice was about 50 m/s, that of Beijumahe sluice was about 25 m/s; (2)Winter temperatures have generally been mostly warm. The minimum temperature at Baoding station was-22.0 °C, and the 3 d moving temperature pole was-10.7 TI. A short-term strong cold snap may be a common pattern for future ice cover generation; (3)In winter, the water temperature decreases gradually along the range, with the lowest water temperature at the head of the drain Taocha sluice being 6.7 °C, and at the end of the canal Beijumahe sluice falling to around 0 °C in most years. The maximum drop of water temperature in the Beijumahe sluice was from 3.5 °C to 0 °C in 10 d, and in the canal section reached 1.7 °C/100 km during the period; (4)The longest ice cover was 280 km in winter 2016, followed by 73 km in winter 2015 and 38 km in winter 2021, and no ice cover was generated in winter 2020 and 2022. Nearly 90 km of Gangtou sluice to Beijumahe sluices is the section with frequent ice cover, which should be a concern. Based on the measured data before ice cover generation, the initial water temperature and interval air temperature model is used to fit the concise water temperature prediction model and the critical threshold of ice cover formation with different forecast timeliness of 2 d, 3d and 7 d. The preliminary analysis concludes that; winter temperature and water flow are the two main drivers of ice cover generation, the lower the flow the lower the temperature the easier it is to generate ice cover, and the short-term strong cold wave in January is more conducive to ice cover generation. The severe ice regime in winter 2016 was the result of a combination of two factors; the winter 2015 ice cover was mainly induced by low water delivery flows, while the winter 2021 ice cover is mainly due to a short-term strong cold snap. © 2023 China Water Power Press. All rights reserved.