Increasing water infiltration – swales & gabions
How to enhance this area:
Swales & Contour ripping
We aim to enhance this area by building swales and do contour ripping (depending on the land of course) which help to reduce groundwater runoff and improve filtration and the establishment of perennials.
Swales can easily be placed on contour using a simple water level (two poles with a 20m aquarium water pipe filled)
In the desert the swales should be deep and wide so that they can hold all the water coming down in the few large rain events. Calculate this by calculating the area between the swales – needs to hold all the water coming down in a rain event of say 50mm.
Beware of animal tracks uphill of the swale – easily blows it out when water comes rushing down the animal track.
Make swales 3 to 4 times larger than you think so it can hold the main rain event (which brings 25% of your yearly rainfall). Plan for the high season.
Speak to Colin Nott of the National Rangeland Management and Strategy Program r
To keep costs low we can deep rip on contour like a swale, then the little water we get will run into our deep rips.
Perhaps we can design a plow that deep rips AND makes a swale in one pass so we have a drainage swale.
Swales & Net and Pan (Microdams)
We will build swales and also implement net and pan systems to maximise water retention and organic matter buildup where possible. We will need to have a bit of runoff for swales to work – if sand is too deep then infiltration is happening anyway. Swales should be max 100m apart. Calculate that they can hold the max 100 year rainfall event so that they don’t blow out. 100mm rain = 1000 m3 per ha. Use a mule and a dam pan.
Anti Evaporation Strategies CRITICAL
– All irrigation water should go into gravel pits close to the plants rather than directly on the ground – this way it can soak in immediately and will be away from evaporation. Measure pH to ensure you don’t get increase in alkalinity through salt deposits.
– Plant wind breaks to slow down wind evaporation
– Consider using closed greenhouses to all but eliminate humidity loss from vegetable production
– See Lesson 24 of the Online PDC
– We can use clay pots in all irrigated fields – to store our irrigation water locally and release it slowly to the roots.
“Bunde” – Micro Swales
In sandy soils such as in the Kalahari the water will just soak away. We’ll need to add clay and organic matter in order to make the soil absorb the rainwater. Then we can store massive amounts of rainwater in the soil where we can use it to plant or we can use it to drip slowly into our dams (which need to be deeper than 3m). Think of the landscape as a huge sponge. Currently its not spongy but we can make it so. (Can we mix the calcrete of the southern Kalahari with the sand to make better soils? Needs research) So we should build tree “nests” with nice soil and use calcrete over the sand to direct the water into these nests?
Here’s a great rundown on possible desert restauration fodder plants: https://desertification.wordpress.com/category/pastoralism-animal-husbandry/fodder/
Yeomans Plow – vibrating – will rip even concrete surfaces