Rainwater Harvesting Methods

What do we need to do with water? Slow it, Spread it, Sink it!

Brad Lancaster: “Rainwater Harvesting for Drylands and Beyond”

The 8 Principles of Successful Rainwater Harvesting

Berm and Basin

Good for planting trees in!

Planting microbasins

Mulching! Organic Matter (dead plants) Living Mulch (ground cover) Rock Mulch

Using hard runoff areas to fill mulched or vegetated retention spaces: paved areas and roads.

Roofs are hard runoff areas

Swales

Swales on-contour

Off-contour Swale…

…aka diversion drains or diversion swales

Wide, level sill overflows (spreader drains)

Boomerang Berms Endpoints point uphill and are slightly lower, allowing an overflow at one or both ends when basin is full. A good idea to reinforce overflow point with rocks.

Cascading More, smaller earthworks will spread out flow and stop overloading Can combine several techniques

Boomerang berms to focus water around trees and contour swales below on hillsides (can link to keyline dams).

The steeper the slope, the narrower earthworks need to be and the more of them we need. On very steep slopes they must be reinforced (with rock or concrete). Swales/ Berm and Basins on Different Slopes

Overflows Pipes can be necessary if a road goes over the top Can also use a permeable stone “wet crossing”

Multiple Functions

Net and Pan Upper half of pan is catchment surface draining water to lower half where water infiltrates into tree root zone.

Check dams Water moving downslope carries with it sediment and organic matter. The faster it moves, the more it erodes and carries. In gullies, erosion can happen fast. Check dams are barriers that make the water slow and pool, depositing its sediment behind the dam, forming a terrace.

Planting into fertile sediment behind dam is recommended – it will stabilize the terrace and is often fertile and good for growing.

Check dams can be used inside diversion swales to control flow rate and erosion

Check Dam Apron

Importance of Planting after earthworks Every time we move soil, we should be ready to follow straight on with planting or seeding. Plan the planting and stabilisation of area before starting the earthworks. Prevents erosion, fertility loss, damage to earthworks. Often fast growing N-fixing species are best.

Understanding Slope and Contour (Maps) Level: flat lines at right angle to slope, curving as slope changes, around valleys and ridges. Where water will not flow Same height apart (intervals) Surface distance apart changes depending on slope Each given a height above “datum” – usually sea level, but can be any other fixed point. Valley floor

Contour in a landscape

Finding contours…

Water levels

Contour Lines

Distance between contours? STEEPER SLOPE: Closer together GENTLE SLOPE: Further apart Vertical drop: Generally, no less than 1 meter for erosion control Surface Distance: If using nitrogen fixing trees, contour hedgerows be no wider apart than 5 meters so alleys get full fertility benefit

Knowing contour lines helps us to control erosion and make integrated water retention earthwork systems… Contour plantings Swales Terraces

Alley cropping with nitrogen fixing trees

Biodynamics, crop rotation and other methods can still be practiced inside this pattern

“Passive terracing” over time… Over time the accumulation of organic matter on the back side of the treelines will naturally form a terrace

Also called “Green Terracing”

Can also be done with swales and berms

Terracing Needs the most caution Progressive failure of poorly built terraces over time can lead to severe land damage Not appropriate in soils prone to waterlogging where rainwater infiltration can lead to saturated subsurface conditions that stop water moving down through the soil (e.g. very heavy clay layers)

Terracing by hand or machine… Smallest version are narrow terraces called “Benches”. Like making roads.

Roads can also act like swales… …or off-contour swales/ diversion drains. They are hard areas so will have less infiltration, but can catch a lot of rainwater to fill retention spaces

Terrace Edges Best way to stabilise terrace edges is to also plant them!

Imprinting Small scale infiltration basins over a very wide area for landscape regeneration. Planted with diverse pioneer seed mix, often in the same machine pass.

Also organic matter blowing across landscape is trapped in bottom of pits – “self-mulching” the seedlings

Where to Use? Abandoned farm fields Building sites Overgrazed rangeland Soils with rock up to 1ft in diameter Slopes as steep as 2:1