Gully head protection by overhanging nozzle type drop structure construction
Diverting flood for warping farm land
Head-ward retreat of gullies in the loess plateau is very serious. In order to effectively control it, local people use overhanging nozzle type drops. A basin for collecting water is built at the top of the escarpment of gully head. Then a 5 m long metallic morning-glory type over hanging nozzle is installed in the gully walls directing it toward the basin. The lower ends of the nozzles are fixed to the walls by means of chains acting as suspenders. An apron of willows to dissipate energy protects the fall bottom.
It is a long-standing tradition to divert the floodwater for warping on plots of farmland in Shaanxi province ever since the Qin Dynasty more than 2200 years ago. Jinghui and Weihui irrigation districts were all built in sediment-laden tributaries of the Yellow River, irrigating 75-300 thousand hectares of farmlands. Diverting floods coming from gullies, streams, villages, watersheds and roads to wrap farm land for the purpose of soil improvement, preserving soil moisture and flood control is an efficient method to comprehensive utilization of water, soil and fertilizer resources for farm land construction, increased agriculture production and soil and water conservation.
The benefits of flood diversion by warping are obvious. Increase in the yield in warped farmland is from 22-39 % as compared with non irrigated lands. In order to get high production of crops; techniques of irrigation should be grasped. The thickness of warping should be controlled. The immersed water should be drained and the inter-till age should be done on time. Within 0-30 cm of the top soil layer, the amount of nitrogen, phosphorus as well as organic matter increases by 71.4%, 19.7% and 40% respectively. The rate of salt elimination is in general 48.6% and may reach 75.9% after warping. The unit discharge of warping should preferably be large enough in order to keep the deposits uniformly distributed.
Drawing of floodwater at hyper-concentration of sediment for warping has proved to be an effective measure to meet the demand of water for plants in arid season. The soil fertility is improved and the farmland could be leveled and reclaimed. Ditches could be filled up and the seepage of the ponds could be prevented. In view of all these multiple benefits, it is recommended as an effective method for sediment trap and flood control in watersheds where soil loss is prominent.