Studies on the evaluation of influences of land reclamation on hydrologic cycle and the conservation in catchments

本研究对一些集水区的土壤和水文因子进行了调查，其中包括大量的小农田开垦的森林，以评估开垦的影响，并考虑集水区的保护。结果是。总结如下.1.复垦直接改变了土壤的性质。特别是表层土壤干密度的增加降低了土壤的渗透能力和保水能力，从而控制了集水区的水文循环。结果表明，农田的洪峰流量可能增加植树次数，直接径流量可能增加两倍于林地。与森林相比，陆地蒸散量可能有所减少。但对长期径流特性的影响可能很小或没有影响.复垦后农田底土和水文因子的变化，可能会使农作物的生长条件恶化。机械压实地下水会使地下水滞留在地下水中。土壤渗透性的降低和坡度的减小可能会中断降雨的排泄，对农作物造成伤害.细沟侵蚀是复垦耕地的严重问题。霍顿定律适用于田间细沟网络，可以用概率模型进行模拟。通过室内试验或田间调查，测定或估算了细沟发生的临界流量，以阐明细沟发生的机理。

In this research, soil and hydrologic factors have been investigated in some catchments, which include a lot of small farm lands reclaimed from forest, to evaluate the influences of reclamation and consider the conservation of catchments. The results are. summarized as follows.1. The characteristics of soil are directly changed by the reclamation. In particular, the increase in dry density of surface soil layer reduces the infiltration capacity and water retention capacity of soils, which control hydrologic cycle in a catchment. As a result, the *peak.discharge from farm land may increase tree times and direct runoff may increase twice as much as that from forest. And the evapotranspiration from land may decrease in some degree, compared with that from forest. However, the long-term runoff characteristics may be influenced little or not influenced.2. The changes of subsoil soil and hydrologic factors in the reclaimed farm land, may aggravate the conditions for the growth of crops. Compaction of subsurface layer by machines will cause a perched groundwater in subsurface layer. And the decrease in permeability of soil and the decrease of slope may interrupt the drainage of rainfall and cause damage to crops.3. The soil erosion by rills is serious problem in reclaimed farm lands. The Horton's law is applicable to the rill network in fields and it is possible to simulate it using a probability model. The critical flows for rill initiation were measured or estimated with experiments in a laboratory or investigations in fields to clarify the mechanism of rill initiation.