pond at watercourse

We are developing a half-acre garden and there is a non-permanent watercourse on the bottom. Apparently it's dry most of the time, but the trees indicate that there is constant soil moisture. So I want to dam it a bit up and since we are using a machine for swales I could dig it a bit wider and maybe deeper. Any thoughts about how to? How to seal? HOw big? The soil is a mixture between clay and sand.

You'll have to turn English subtitles on. Will this work?

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So that debri does not fill and dam or pond you create, having it off stream is an important issue to think about.

Does anyone have experience with compacting or gley or lawn?

I could not find an English sub title.
But I understand what is being said. I work in the area of water catchment as a Civil Engineer.

A series of small embankments running up the stream will capture water and allow it to soak into the ground, much the way it did before mankind 'tidied'
all the rivers and streams up.
Banks need to be protected from over flowing, thats why the spillway is set lower than the dam top and taken away from the earthworks.
It is often lined with stones etc.
The banks need to be wide to ensure collapse does not occur.

Your question about compaction etc needs expanding please?