fantastic artice on principles of dry water bed in japanese gardens here:
http://findarticles.com/p/arti cles/mi_m0NTB/is_9_43/ai_n5996 117
It even tells hoe to use stone sizes to create the illusion of fast-moving water and slow moving water...
Use rocks to create interesting effects, such as the dry pond in the photo at right. This was made with Mexican river rock and oolite (coral rock) stepping stones. There is a Clusia nana on the volcanic rock in the middle of the pond. This landscaping feature needs neither irrigation nor fertilizer!
Stone is a very important feature in a Japanese Garden. Dry landscape gardens sometimes contain little more than carefully place rocks set in a ‘sea’ of gravel. Stones can point upright, symbolising mountain peaks or be laid on their sides to form a bridge. The Japanese never use a ‘diseased’ stone which is misshapen on top, or a ‘dead’ stone which is an upright stone laid horizontal, or a ‘pauper’ stone that has no visible relationship with other stones. Stone placement today still follows principles laid down over a thousand years ago.
A dry slate gorge represents a watercourse in our garden and a boulder bubbling water symbolises an active volcano. Raked gravel represents waves and the sea.
more here --