development of warping dams on the loess plateau
Abstract - Valuable farmland can be created with warping dams by trapping eroded soil flowing down a gully during the flood season in the land-scarce, badly-eroded loess plateau. Not
only would the dams conserve soil and water for local economic development, they also help to reduce excessive sediment deposition in downstream rivers. Fully implemented a large scale warping dam program provides a long-term solution to Yellow River's sediment problem. How best to utilize the warping dams to make them attractive as financial investments under a market economy is a key issue to the success of the program, and is the topic to be discussed here.
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Urgency for sediment control
The loess plateau in China's Yellow River middle basin is one of the world's mostly badly eroded regions in the modern time. Extending for an areas of 430,000 sq km, the loess plateau contributes over 90% of the 1.6 billion tons of the total sediment carried by Yellow River annually. To control sediment production from the region we might first target areas identified as "severe eroded areas," whose annual erosion rates exceed 5,000 tons per sq km, for a total area of 156,000 sq km, contributing to 83% of the river's sediment load. Some areas have erosion rate reaching as high as 30,000 tons per sq km. Targeting the severe eroded areas is just a stop-gap measure attempting to reverse the continued deterioration of the conditions of the river, and to prevent flooding in the downstream densely population region. This paper once again emphasizes the importance to control erosion in the loess plateau, since new opportunities to finance such an effort opens up as the nation enters into a new economic environment.
Let us recall that when the Sanmenxia dam in the river's lower reaches was completed in 1960, sediment accumulation in its reservoir threatened to deplete its storage capacity in a few years. Consequently, the Sanmenxia dam had to be redesigned to include sediment-flushing facility to clear its reservoir of sediment accumulation, delaying its normal operation schedule till 1974. Presently, roughly 1/3 of Yellow River's annual flow is used for sediment flushing, and in so doing, 3/4 of the total sediment flow is flushed out to sea, leaving behind 1/4 of it, the coarse-grain sediment, to silt up the downstream river channel steadily. After thirty-some years of sediment accumulation, Sanmenxia dam's reservoir no longer has the capacity to temper a flood peak to protect safely the downstream diked region. Consequently, the Xiaolangdi dam is being built upstream of the Sanmenxia dam to afford safety to the densely populated downstream region. Even with sediment-flushing proviso, the Xiaolangdi dam is expected to have a very limited useful life, if sediment deposition in the river remains unchecked. What then is the long-term prospect for Yellow River?
Returning to the strategy for erosion and sediment control in the loess plateau, opinions on how best to carry it out differ widely. On the one hand, it is advocated to implement an extensive and comprehensive water-soil conservation program over the entire land surface with terracing of cultivated hill slopes, planting of trees, shrubs, and grass to retard surface erosion, as well as legal ordinance limiting human activities to prevent the destruction of forests and herding of sheep and goats. On the other hand, others argue in favor of the relatively simple proposals of just stopping sediment flows coming out of the gullies and minor river tributaries, and preventing them from reaching the major rivers.
In my opinion, while it is perfectly sensible to implement a well-planned water-soil conser
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