well i can offer this totally unhelpful fact - ukemi work great on beach sand, this discovered last summer being an idiot on the beach with some friends. I have yet to figure out how to do ukemi under water!

well i can offer this totally unhelpful fact - ukemi work great on beach sand, weather you slap the sand or not this was discovered last summer being an idiot on the beach with some friends. I have yet to figure out how to do ukemi under water!

Ukemi allows for duel participation
 

Funnily enough it seems to me that Ukemi is primarily to allow the uke to receive and remain uninjured from receiving sometimes awkward and potentially lethal counter attacks from the Nage.
I think much of the Ukemi practice is to this end. You can roll from virtually any throw that ends with the nage releasing the Uke. If the Nage wishes to hold onto the nage such as in some types of Shihonage or Kotogaeshi for example then you have no choice but to break fall using a slap wether that be from the arm or in some instances from the feet. There are few people anxious to try to roll out from an "over-the-top" shoulder height Shihonage.
I feel that many techniques in a "street" situation wouldn't involve an uke that was either willing to receive a technique or even be able to preform Ukemi anyway. Thus most of what we practice is really a facilitation in aiding both the Uke and the Nage to learn valuable lessons simultaneously without having to slow a technique to a crawl or applying some sort of non-contact simulation of the technique. Both approaches have little application in true Aiki from my perspective. Additionally the Harmony/Love aspect of Aikido couldn't be practiced if we are intentionally out to dominate and destroy our practice partners. The street is a totally different environment to the dojo.
Obviously there are other benefits to Ukemi waza besides just being a practical way to avoid damage to ourselves but that is another discussion entirely.

Take care and God bless

Marten Coombe New Zealand Aikidoka

Welcome to E-budo, Kiwi Aikidoka!:)

[edited out of stupidity and blindness]

Back to ukemi. I understand what you are saying concerning ukemi in the practical sense, but this thread seems to have two purposes: ukemi for defense, and ukemi for defense against the ground, be it cement, wood floor, dirt/grass, sand, and, well, water, too I suppose.

It seems the one manner of which most people have the habit of doing, is falling at the strangest of times, with ukemi being a life-saver, or serious injury protector, so it does fall into the practical manner of ukemi, whether the attacker is tori, or you yourself are put in that situation because you forgot to tie your Nikes.

So I don't think a practice now and then on harder surfaces than tatami, is necessarily a "different subject."

Stuff happens.

Mark