I'm pretty sure everyone knows that collecting a large amount of glass can lead to some really ugly landscapes where pretty much a large, stone hole is left after you take all the sand from the beach. I want to avoid this - keeping my world as naturally nice as possible. I am pretty certain that there are no real desert biomes in a reasonable distance around me (~500 block radius).
How can I harvest lots (> 10 stacks) of sand for glass/sandstone without leaving huge craters in the landscape?
Focus on breadth, not depth.
Skim a layer or two off every beach you find. You'd be surprised how for down the sand goes - it'll still look natural after you've collected all you need.
I think that unless you're able/willing to use console commands to spawn sand, the only way to obtain sand is to get it from the landscape.
You could 'cheat' the look of the landscape though - tunnel to the sand from underneath, take as much as you'd like, then build a platform out of rock (which is self-supporting), and lay a single block thick layer of sand on top to make it look like a sandy area! :)
I went in a straight line until I found a pretty large sandy area and started by covering a section of sand over with dirt. I then dug out all the sand underneath the dirt and made myself a tiny base.
During the day I'd go up and lay more dirt over the sand, then at night I'd go into this vast cavern with 10 ovens and dig out/cook stack after stack of sand. I'd also dig off a layer or two of dirt in order to give me more dirt with which to cover over the top.
When I hit one water edge where the land fell off rather quickly I made a huge glass underwater wall. This looks fantastic. At the bottom I built it so that the water comes in under the glass and forms a little pond so that I can just jump into the water and walk under the glass to get out.
This huge open cavern has become a massive town center sporting a railroad hub, a huge automated grain farm and the ongoing sand mining operation that tends to supply many of the players on the server with a nearly infinite supply of glass.
Above ground it's just trees an dirt as far as anyone knows. One tiny tower allows railcars from "town" to spiral down underground, but otherwise you'd think you were in the wilderness.
It's no longer sand, but it doesn't look any worse than any other dirt beach, it protects the beaches near town by supplying glass for anyone who needs it and it created space for a really nice base. win/win/win
Just go to a place far away that you won't got to unless you need materials.
For tips on how to travel long distances see this question: What is the fastest way to travel long distances in Minecraft?
I actually just extend water edges when I need sand.. I built a small little bay and excavated quite a bit of sand for use as glass (Id say around 5 or so stacks). This got me a large stack of glass, and compliments on how neat the little bay was. I can take screen shots if it would help but its a bit of a walk from where I am now in the world.
Two ways in your situation:
First, clearly you're a homebody if you consider walking 500 blocks to be "too far"—so use this to your advantage! Just this once, take a very long walk to find a desert biome, and strip-mine the poor thing for its precious, precious sand. Then take your sand home, safe in the knowledge that you'll never see that desert again.
Secondly, you can easily mine sand off the ocean floor without noticeably altering the look of the land:
Digging underwater is slower than on land, so to speed up digging you can bring many doors and place them strategically, digging while standing inside the air bubbles. Equipping an Aqua Affinity helmet allows you to dig underwater at normal speed as well.
Since you're not in a sand biome, you could go ahead and dig out all the sand, then repair just the top layer with dirt (which isn't affected by gravity of course). This is a quick-and-dirty way to get the sand and still have a tidy landscape.
You could set up a cobblestone generator by putting a lava source block and a water source block in a 4-block long trough.
The generator will ensure that you don't ruin any other parts of the landscape when you go mining for stone.
Then with your cobblestone you can fill in the hole you leave when you mine all the sand out of it.
It'll look like a natural pebble beach instead of a sandy beach :)
Go underwater, place two fence posts on top of each other with a jack'o'lantern for light to make an easily findable air pocket. You can then dig as much sand as you want. Also if you use signs (from the post outward) you can extend the air pocket in a way you can walk through, and you can place signs on top of signs to create underwater walkways. This is also a very good way to harvest clay too. Be careful though when layering signs, because if one is broken it will cause every subsequent sign after that to drop too. Try not to make your underwater walkways too big, otherwise creepers can spawn down there and destroy your entire walkway past the point they explode. Doors also make good air pockets, but unlike signs, you can't pass through doors, so you have to be a bit craftier about making it navigable.
