因此，他们的第一个日历系统被自然地分为三个季节，每个季节都是根据河流的变化而划分：淹没期、下沉期和丰水期。

So, naturally, their first calendar was divided up into three seasons, each based on the river's changes: inundation, subsidence and harvest.

youdao

第一个季节是洪水泛滥季，这时候的尼罗河流域基本上会被水淹没几个月左右。

The first season was the flooding, or inundation, when the Nile valley was essentially submerged in water for a few months or so.

youdao

河流在暴雨季节冲破堤岸，形成新的河道。

Rivers break their Banks under seasonal downpours and carve new paths.

youdao