17 Ridge Versus Valley Dams


Ridge Versus Valley Dams Tom Ward: For every key point there is a bench
on an adjacent ridge. So it is better to build your – ponds out
on these benches, on adjacent ridges and divert water. Then you don’t blow out in a flood, then
you don’t have to build giant spillways, then you don’t, then you have enough material
for your dam, and less bulldozing time for bigger capacity. So the other reason you don’t build a pond
in a gully, is because you want slopes that are less erosive, and you want to be able
to drive all the way around the pond to rebuild the pond every 10-20 years. That’s mucking out the pond, we do that
with the excavator on tracks. You can’t do that in a gully. So gully ponds tend to have 1:1 sides, 1:1
dams, and that’s unstable, and they fail. Wave action, landslides, big events. So between not having enough soil to build
the dam and having to borrow it from some place else, having to build a heroic spillway,
that goes either right over the dam, which is idiotic, you have to cement it and stuff,
or it runs around one wing, really difficult. So thee spillway’s difficult, the slopes
are bad, a good pond has a 3:1 slope on the inside, a 2:1 slope on the outside, and most
of the ponds I build had to compromise. And I went to 1:1 on the outside and 2:1 on
the inside, which is as steep as I would ever go, and I was like, “I can’t guarantee
this pond”. And the ponds that I’ve worked with the
longest, like the last resort, we have now rebuilt it for the second time. We built it in 1980, we cleaned it out in
mid-90s and we just had to clean it out again. And that’s because of cattails and biomass
and muck and so there’s, so I like to have ponds, like a saddle, where you can drive
all the way around the pond with an excavator. With a long arm, and you can muck out this
pond whether it has water in it or not. And then the other thing with ponds is your
lock pipe. How do you get the water out of the bottom
of the pond for irrigation? And if you’ve got a really steep sided pond
with a lock pipe in it, you’re likely the leak. And oh my god, what are you going to do then? Camera Man: It’s a bit of a baffle but even
then you… Ward: Even then. So I prefer siphons to lock pipes but I like
to have a drain pipe in so you can drain… Darren Doherty: Cattails are a great thing
to have around the edge of the pond, but if you don’t have a sharp angle at the edge
of the water, they will continue their march into the pond until the whole thing is basically
a wetland not a pond. That’s the succession that they, they’re
an awesome organism. Man: Clean them out of there, by hand. Doherty: The ideal pond from my perspective
is where on the edge of the pond, when you say work in for the first two or three meters
of the edge, that you have a 1:3, 1:2 bed and then you go in steep to 1:1. Now the reason for it is that you can get
cattails and fragmites and all the usual suspects, growing around the edge so they buffer the
waves and also do their nutrient cleaning job, which they’re fantastic at doing. But if you get that dive in quite steeply,
they just can’t cope with that as being a place to establish themselves, right?

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