[Tursiops2]

Hi ilia.
Apologies for being frank, no offence is intended, but although your design contains most of the essential components of a wild life pond, I don't think it makes anything like the best use of the space you have to work with.

There are several points to bear in mind:
1. The maximum bio-diversity of a pond occurs in water less than 5cm deep, and most of your pond appears to be more than 30cm deep.
2. Water over 1m deep in a small pond is, effectively, ecologically sterile. A max. depth of 70cm should be sufficient - don't give yourself unnecessary work to do.
3. Water absorbs oxygen from the atmosphere as well as gaining it from submerged plants. A simple geometeric shape maximises the surface area, as well as being easier to excavate, construct and maintain than an irregular "organic" layout and, in my opinion, looks better in an urban or built-up setting.
4. Every "garden" pond should have an area of non-slip hard-standing on one side, to allow for safe access and maintenance. This is even more important in a school pond where pond-dipping is a regular activity.

I’ve not had the chance to put this into practice, but for what it’s worth, in your situation I’d do the following: allowing for site-specific constraints, dig out the biggest rectangular trench practical, to a depth of 30cm- 40cm, with a small area down to 70cm; line it, and then partly backfill with a suitable low-nutrient substrate which can then be contoured to create an irregular shoreline with areas of varying depth and slope, rising above the waterline round the edges. I wouldn’t bother with extensive shelving for pots when planting on that scale.

I’d also put a spacious area of timber decking along one side. Overhanging the water by a few inches to create a shadow line, this could also conceal the outflow pipe.

Waterfalls or cascades are good for a wildlife pond (they help oxygenate the water and can add to the range of habitats) but they’re difficult to construct so that they look “natural” if you’re not on sloping ground. You could use the spoil from the excavation to build an embankment around one end of the pond to set a cascade into; and if you want waterlilies, contour the substrate to create two discrete compartments separated by marginal vegetation, one for the cascade and one for the lilies

As for the actual digging, it’s a mattock + shovel + barrow job, best done by two, or even three, people. If you’re doing it on your own, be methodical; work from one end to the other, taking it down in 15cm-20cm spits about a metre wide. Make sure you’ve got somewhere to put the spoil, and a safe and unimpeded barrow run to get it there.

Are you anywhere near Ipswich? I’ve got free time at the moment, if you’re reasonably local I could give you a hand with this.

Tursiops2