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

在本研究中，研究了一些流域的土壤和水文因素，其中包括大量的小农田从森林复垦，以评估复垦的影响，并考虑流域的保护。结果是。总结如下：1。开垦直接改变了土壤的特性。特别是表层干密度的增加，降低了控制流域水文循环的土壤入渗能力和保水能力。结果，*峰值。农田的排放可以增加树木的数量，而直接径流的增加可能是森林的两倍。与森林蒸散量相比，陆地蒸散量可能有一定程度的减少。但长期径流特征可能受影响较小或不受影响。复垦农田的底土、土壤和水文因子的变化，可能使作物生长条件恶化。机械压实会造成地下地下水在地下滞留。土壤渗透性的降低和坡度的降低可能会中断降雨的排水，对作物造成损害。在复垦农田中，沟沟侵蚀土壤是一个严重的问题。霍顿定律适用于野外沟网，可以用概率模型对其进行模拟。通过室内实验或野外考察，对细沟起裂的临界流量进行了测量或估算，以阐明细沟起裂的机理。

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.