并且，由于它们是在地下形成的，而不是由地表水流形成，所以并不是所有的通道都有通向外部世界的开口。

And, since they were created underground and not from flowing surface water, not all these passageways have an opening to the outside world.

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根据DEM数据，确定了汤旺河流域的地表水流方向、集水区的划分及水系网络空间分布特征。

On the base of the DEM, the spatial distribution of flow directions, watershed boundaries and stream networks of Tangwanghe Catchment were studied.

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基于田间实测的地表水流推进过程，利用水量平衡法推求波涌灌溉间歇供水条件下的土壤入渗参数。

Based on water flow advance data observed in fields, infiltration parameters under surge water application were determined with water balance method.

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