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

在本研究中，我们调查了一些小流域的土壤和水文因素，包括许多退耕还林的小流域，以评估开垦的影响，并考虑到流域的保护。结果是。总结如下：1.围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入渗能力和持水能力，而土壤的入渗和保水能力控制着流域的水文循环。因此，农田的峰值流量可能会增加树木的次数，直接径流量可能会增加两倍于森林。与森林蒸散量相比，陆地蒸散量可能有所下降。但对长期径流特性影响较小或不受影响。复垦农田土壤和水文因子的变化，可能会加剧作物的生长条件。机械压实地下将导致地下水滞留在地下。土壤渗透性的降低和坡度的降低可能会中断降雨的排泄，对农作物造成损害。细沟侵蚀是复垦耕地面临的严重问题。霍顿定律适用于田间细沟网，可以用概率模型进行模拟。为弄清细沟形成的机理，通过实验室实验或野外调查，测量或估算了细沟形成的临界流动。

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.