Sorry it has taken so long for anyone to respond.....not a very active forum :-))

Dry stream beds are very popular landscaping conventions, whether used for actual water run-off during the rainy season or not. The trick is to make them look natural, which means not laid out in a straight line but with some natural curves to adapt to the land contours.

Typically they feature river rock (a smooth, rounded rock of variable size) and need a few larger rocks to provide that natural look. And they need a defined beginning and end - they just can't spring out of nowhere or end abruptly.

Here is a good example of what one should look like, including the larger rocks/boulders and accompanying plants:

garden web photos · More Info

If you Google "dry stream bed design", you should find inspirational photos and examples as well as how-to instructions.