Tuesday, December 01, 2015

Allotment Winter Jobs List & Rainfall Calculations

It occurs that I've never actually dug very far down in the NE bed. I just turned it over once, before sowing the phacelia. So that's a spit, about 10ins. The way it's getting so waterlogged, it might well be the case that the clay is just below that. So:
  1. Do a test dig in NE bed, 4yds sq, see where the clay is.
  2. Dig a couple of spits down into the clay. No need to worry about gently sloping sides for froglets, or puddling, (yet), just get a hole in the ground for all that water to run down into. 
  3. Widen trench and relay path, with foundation of 3 or 4 courses of bricks to help drainage. Path should be raised somewhat. 
  4. If drainage is working, so I'm not sinking into the earth too much, dig down into clay on NW side. 
  5. Join NE and NW ponds, now paying attention to puddling and getting slopes good for wild-life. Maybe build a bridge in line with path. 
  6. Go back to levelling and removing foundations in Old Greenhouse area. 
  7. Tidy up Southern end, (lay path, level, dig out midden; if time permits, sort out shed). 
Still on course then to be all drained and level for the next growing season. Not sure if drainage holes at Northern end are going to result in a pond or a bog - bit of both, probably, which is more natural anyhow. I hope it stays enough of a pond into summer to allow tadpole metamorphosis.  I recall the North end being really waterlogged last July. So, given the Glasgow climate, it all might just work out. See the chart, (from Springburn weather station, just over the motorway from the allotment).

The lowest rainfall is April, 80mm, so about five inches. To keep tadpoles alive and happy, we need about 18 ins of water, over the ponds central area, let's say 36ft sq. (Deploys calculator). That's a bit over 5000ins sq, times 18 for the depth, and we get 100,000 cubic inches needed in the pool. Bear with me. 

The whole allotment is 90x30ft. That's... 2700sq foot, times that by 144 and you get 388800 square inches of allotment. Onto each inch falls 4ins of rain, even in the driest month. That's about 1.5m cubic inches of rain. The path will be arranged to drain into the pond, but naturally a lot will be used up by plants and evaporation along the way. However, if only 7.5% of the total rainfall falling onto the allotment finds its way to the pond, then we're home and dry. Well, wet, actually. We can validate my calculations next year. My money's now on a pond, rather than a bog. 

The things doctoral students will do when they should be working on their research...