The Huai River is one of major rivers of China, originating in Taibaiding (also named Dafufeng), the highest peak of the Tongbai Mountains in Tongbai County, Henan Province, and flowing west to east through southern Henan Province, northern Anhui Province, and northern Jiangsu Province, and emptying into Hongze Lake. Most of the water reaches Sanhe Floodgate and empties into the Yangtze River through Sanjiangying, Jiangdu city, Jiangsu Province, while a small amount flows into the Yellow River through the Northern Jiangsu General Irrigation Works. In flood years, the water flows into the Qishui Basin through the Erhe Floodgate and into the Xinqi River and finally empties into the Yellow Sea. The Huai River is one thousand meters long and covers an area of 269,000 square kilometers. The stretch of the river extending from Heyuan to Honghekou are its hilly upper reaches with wider courses. From Honghekou to Zhongdu lie the middle reaches with slight gradients, winding courses, and slow currents. The terrains of the river banks are flat, scattered with lakes and low-lying land. The lower reaches lie east of Zhongdu, where the courses are wider and shallower, with crisscrossing water networks and lakes of different sizes. Due to the unique geological structure, tributaries on the southern bank are shorter while those on the northern bank are longer, making a water system with an asymmetrical distribution. Most of the Huai’s tributaries on the southern bank originate in the northern Dabie Mountains; these include the Shi River, Zhugan River, Huang River, Bailu River, and Shiguan River. Most of these rivers are shorter with rapid torrents and large water capacity, typical features of hilly rivers. The rivers on the northern bank originate in the hilly regions west of Henan Province. A few of them originate from the flatland south of the bank of the Yellow River. These major tributaries are the Ru River, Hong River, Ying River, Xifei River, Wohe River, Beifei River, Hui River, Tuo River, and Sui River, which are long and crisscrossed. The Ying River is the longest tributary of the Huai River. The Xifei River is connected with the Ci River and Wohe River, while the Hui River is joined with the Tuo River, and the Tuo River is linked with the Sui River. Its tributaries on the southern and northern banks differ due to features in geology, climate, and soil. These rivers also have distinct hydrological features. Topographically, rivers in the south are classified as mountain rivers, while those in the north are known as plains rivers, which have winding courses and slow torrents. The area south of the Huai’s tributaries has a wet climate with annual precipitation of a thousand millimeters. These rivers have high capacity and plenty of run-off. The average temperature of the coldest month there is above 0℃, so these rivers do not freeze in winter. The northern bank of the Huai has a warm semi-humid climate with annual precipitation of six hundred to nine hundred millimeters. There is not as much run-off in the north as in the south, and the run-off is more variable. The average temperature of the coldest month is below 0℃, so in winter, rivers can freeze. Originally, the Huai River emptied into the sea without tributaries. At the lower reaches it takes in the water from the Si River with its tributaries the Qi and Shuzhu Rivers, and it empties into the sea at Yuntiguan Pass. In 1128, the Yellow River invaded the Si River near Huaiyin, and then the Huai River, and emptied into the sea. As a result, the riverbed at the lower reaches is elevated due to sediment deposit, the middle reaches have become very shallow, and there is a thick deposit of silt in the river basin of the lower reaches leading to the sea. The water system of the Huai River is rather complex. Water levels rose and low-lying lands have become lakes which connected with each other and evolved into Hongze Lake. In 1855, the Yellow River burst at its northern bank and emptied into the sea at Lijin. Originally, as the Huai River has no drainage trunk at the lower reaches, water rose in the flooding season and dam bursts occurred, causing great damage. After the founding of the People’s Republic of China in 1949, an integrated Huai River control project was launched. At the upper reaches, Meishan Reservoir, Foziling Reservoir, and many other reservoirs of different sizes were built. Pishihang Irrigation Works were also constructed at the river’s upper reaches. At its middle reaches, flood storage and detention projects were also carried out. Projects like the Northern Jiangsu Irrigation Works, New Huai River, New Bianhe River, and Sanhe Floodgate were also introduced to broaden the seaward course. These projects have contributed to the reduction of losses caused by flooding and help store water.
