I talked with Jimmy Houston on the topic as it pertains to gravel beds. He suggested a tip he has used. He used some landscape fabric over a natural sand bottom and then placed several inches of pea gravel over the fabric. This helps keep the gravel from sinking into the sand and acts as a good bass and BG nesting area prior to the water being warm enough to swim. This is what I have done in a 5 foot deep area just off my dock.

Mike