Thanks for the comments, guys.
The latex river is by an Aussie company called Miniature World Makers. The only thing I've done to tart it up is to trim the reeds, which I thought were a bit too long.
I'm hoping my colleague will have got some good photos of the game, but he is busy with a course at work this week, so not sure when he'll be able to go through them. He also set up a tripod with a time lapse video camera for the whole game - I'm itching to see the result.
So far as the rules went, I'm still not sure exactly what we did wrong in Sharp Practice, but something didn't ring true about how effective the Maori fire was in the attack. We had the Maori acting in skirmish, feeling that this would be about right as the rules say Indians act like this. However, they seemed hard to hit by the British garrison. And yet they seemed to impose an awful lot of hits on the British, despite the latter being in cover. So something was a bit unbalanced there. I wonder if it might have been because, in an effort to keep things simple, we didn't use the Sharp Practice card at all - and so the British didn't get any extra shots away.
Another mistake we made was to regard the British garrison to be in line behind their wall, despite being just a single Group. I'm not sure what the advantage of a line is, but it certainly seemed to add to the casualties the line itself received! I realise now that we forgot Formations can only be formed by more than one Group, so they couldn't have been in line in this case anyway.