Editing Land-Canal Building Question

I love Second Life!
I want to hollow out a trough on my land, so that I can put in water, and build a working canal lock, to demonstrate it to people who love these things.
I have tried to edit my land, and things get VERY uneven and bumpy. I have to redo my house, because it is in the air now, etc.
What I really want to know, is if there is a way to raise and lower the land with precision. I saw a pool created for a jumping whale in Elven Glen that was just what I want.
Thank you to anyone who can steer me in the right direction for resources on this.

More than likely, the pool you describe was created with prims that were textured to look like land.

Actual land is very imprecise. It often appears as different shapes from different camera angles. As best I can tell, this is because the polygons used for land are huge, which makes it easy to create shapes that cannot exist in real 3D space. As a result, the shape appears to "pop" from one state to the next as the camera moves. This is common with low resolution polygonal surface modeling.

If you want your canal to have precise hard edges, construct the whole thing out of prims and then texture those prims to look like land. You'll find the base land textures in your library, or you can take screenshots of the ground and use them as textures.

If you use actual land, you'll have to accept some imprecision. You'll find that it's a little more precise if you use all straight lines and you build in 4-meter increments (easy to see those increments by using the Select Land tool on the editor), but it will never be perfect.

Another way to do this is by editing terrain .raw files. Unfortunetally, you must be the estate owner. But if you are, you can use photoshop. It's quite easy once you get the hang of it. Basically, you paint with different shades of Grey, Black is 0 elevation, white is 100m.

I have been playing arround with these for the past two days - its really fun. I have a river, giant mountains, and a few gulleys.. really nice.

One way to stop the wide effect of land moving is to have an alt buy 4 x 4 partition of your land from you and then terraform that via the alt. Repeat for other 4 x 4 plots. Then combine it all again! Hopefully the individually aligned ground levels will not move again.

That doesn't help much. If you have terraform abilities, what you do at the edge of your parcel can and will affect the neighboring parcels, even if you have no rights on that parcel.

I will agree that for demonstrating a working canal and locks, you want to use prims.

If you try it with terrain terraforming, make SURE you are in a sim that isn't limited to a +/- 4 M terraform limit (which is a problem on most Mainland parcels). You'll have far more luck on a private island, where you have a +/- 100 M terraform limit.

Flatten an area of land.

Select a 4M wide strip of land, as long as you want for your canal. When you're getting started, stick to what is possible by selecting strips of 4M x 4M areas. Making a canal on a diagonal or that follows a winding course is advanced terraforming, and very difficult to do well.

Repeatedly use the "lower land" button in the teraforming pallette to lower the selected section to the depth you want. Use "raise land" button if you go too far.