Delta development and artificial land creation with sediment
Sediment is transported to the river mouth and construct the delta. If the ratio of the annual sediment load to the annual water is high and the tidal currents are weak, a male delta develops and the river mouth is moving into the sea. Male delta is unstable and has only one or two channels flowing into the sea. If the ratio is low and the tidal current is strong, a female delta develops. Female delta is stable and has multiple channels and numerous islands. The aquatic ecology of female rivers is much better than male rivers.
The economic development of deltas has resulted in extremely high price of land. Artificial land creation with sediment has been practiced in many deltas. In the Yangtze, Pearl and Haihe river mouths high speed economic development and convenient shipping accelerate artificial land creation by using sediment deposited in the estuarine areas. The Yellow River provides plenty of sediment resources, and land is created at the delta naturally and artificially. In general, the efficiency of artificial land-creation is about 10 times of natural land creation. The total area of artificial land in China has exceeded 10,000 km2. About 60% of the 18,000 km long coastline of China have become man-made coastline due to reclamation and land creation.
There is a lack of land in mountainous areas in southwestern China. Sedimentation in barrier lakes made the river valley wide and flat, creating land for agriculture and residence from mountains. The rate of uplift Himalaya Mountains is different along the Yalongzangbu River valley forming several rock barriers. Sedimentation has occurred in the low uplift rate sections, while stream bed incision has occurred in the high uplift sections. As a result, about 500 billion m3 of sediment deposited in the high mountain river valleys over last million years and more than 3000km2 of flat land have been created. The same stories occurred in other river valleys in western China due mostly to sedimentation in landslide dam lakes.