Simple tools and El Nino
Two simple tools you may need one day:
To check whether your irrigation nozzles are worn (sprinkler or pivot), cut a 15cm length of plastic strapping tape into a long taper – 2mm at one end and 8mm wide at the other. Slide the narrow end into a good nozzle and note how far it can go. Now slide into other nozzles and, if it goes further the nozzle is worn. If you want to check your pivot nozzles, there is a chart on the Internet giving the Internal Diameter of every nozzle. You can set a vernier for each size, slide the plastic wedge into the vernier and mark a line for each nozzle size. Again, if the wedge slides further into a nozzle 26 than it should, then the nozzle is worn and should be replaced. Our pivots are 10 years old this year, so the nozzles are probably overdue for replacement.
The second tool I made for my small scale neighbours who are repairing/building new dams. It consists of a long straight lath about 2m long; roughly in the middle, two shorter laths are attached so as to make a triangle; from the apex of this triangle you hang a plumb bob, which is on an adjustable length string. The shortest length of string hangs straight down, when the long lath is level – to a mark that shows when the lath is level. They use this for leveling the wall and the spillways – which they call the runout. Then I put another mark for a 1:10 slope which is the steepest I will let them build down the slope of the spillway. With good grass and over a short distance, that should allow water to spill without erosion. Then two further marks give them the 1:1/2 slope of the back of the dam wall and the 1:2 slope of the front. To reach these marks, the string of the plumb bob has to be lengthened – I use something like a guy rope on a tent. If the three laths are held together with verandah bolts it can be dismantled and carried on a bike.
I have found river flow data for Vic Falls from 1907 to 2006 and there is NO correlation between El Nino years and river flow. So we cannot say that, because of El Nino, there will be low flow this year. What is interesting is how variable the flow is, even from one year to the next. I am still hoping to get more recent data…from 2000 to 2006 the average is definitely climbing, but it would be interesting to know if that trend is continuing.