However, the unstable flow is usually considered as stable flow in the calculation of natural river water surface curve in order to minimize the calculation work.

但在天然河道水面线计算中，为了节省工作量把不恒定流视为恒定流。

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If you swim in a river or lake, be sure to investigate what is below the water surface.

如果你在河里或者湖里游泳，一定要弄清楚水面下有什么。

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Water on the land surface appears in shades of dull green, and a temporary river runs north-south through the image.

陆地表面的水流呈现暗绿的阴影，一条临时出现的河流自北向南纵贯图片。

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Malton, Old Malton and Norton are defended from the river but surface water and backed-up drains have flooded several properties in the area.

BBC: Road to Brawby

Residents said they were concerned that problems were caused by surface water and river flooding.

BBC: Drainage study for flood-hit Tirley to go ahead

He says the hippo sprang from the water, furiously attacked the canoe, then slipped back below the surface of the river.

NPR: Congolese Hunt 'Osama' the Hippo