One of the most interesting challenges of my early career was being involved in on-farm plan development for large scale drainage programmes on the West Coast of the South Island of NZ.
The main obstacle to farming in this temperate, very wet environment with up to 8000 mm of rainfall falling onto the mountains of the Southern Alps and 2000- 4000mm on the farmed areas was to manage the water away from the root zones of the pasture plants so that they could grow rich temperate pastures for dairy cows.
One of my first challenges was to devise 12 Drainage farm plans for farmers who farmed the Kongahu Swamp area of 800 ha just south of Karamea on the northern end of the West Coast. The Kongahu Swamp was a privately owned long narrow peat bog that had formed behind sand dunes to the east of the Tasman Sea .
It was a genuine peat bog, and I still recall the eerie experience of trying to scramble around to survey the swamp and how, every step that I took on the peat was like “walking on water”. Great ripples of saturated peat moved outwards as I put my foot down in a forward motion. It was OK as long as I stayed on the surface but as soon as I broke through the crust of the peat, I sunk, (ingloriously!) up to my waist into the bog!!
At the time I can remember wondering how we could ever drain the swamp sufficiently to develop dairy pastures on the peat, but such was the ingenuity of the drainage contractors that they floated hydraulic excavators into the area on huge log mats, which dispersed the weight of the machines out over the peat and enabled the digging of the network of main drains that started the drainage process. Not that the drainage was without incident - I can recall three or four occasions where excavators fell off their mats and sunk completely into the peat bog so that all that was showing at the surface was the end of the excavator bucket arm! They managed to recover most of the excavators eventually and restore them to operating order but it certainly wasn’t a job for the unadventurous.
The Kongahu swamp is now thirty years later completely tamed and supports some highly productive dairy herds. The farmers have in that time learned how to manage their peat so that they don’t over-drain the soil leading to organic matter breakdown and lowering of ground level. Because they were so close to sea level in the first place, they have also installed tidal floodgates so that large tides do not cause flooding of the peat swamp with salty water.
