This map shows the outcomes of gold mining race building restrictions
On this map you can see two water races following a contour around the hillsides.
Without access to timber and other materials for aqueducts and with limited cash to build them, race builders (known as diggers here in New Zealand in the 19th Century) were forced to follow a contour right up into the gullies and back out again to maintain the desired fall and in doing so loos "altitude" in the gullies marked "a" where substantial streams flowed, the race would almost certainly have been designed to "pick up" water from the stream it crossed and bridging the stream lower down its watershed might have been counterproductive, but at the places marked "b" where no water would have been available, crossing the gully with an aqueduct would have saved digging and loss of altitude.
On the Oamaru Borough Race where there was no need and certainly no desire to pick up stream water along the way, every small stream was crossed with an aqueduct to keep the river water in the race uncontaminated.
The Engineer (McLeod) will have crossed the gullies at the most economic point - not too far up (just to get the aqueduct as short as possible) because loss of altitude was important to eliminate, nor not too near the mouth of the gully where the minimum altitude loss was to be had, because there the aqueduct will be the longest.
The balance would also be affected by the condition of the sides of the gully - if they were steep and rocky like at the Awamoko Creek then crossing right at the mouth was necessary - even if the aqueduct was long contrasted with Horse Gully Creek where the sides of the gully were gently and easy digging, and despite the loss of altitude, a short aqueduct right at the head of the gully was appropriate. Note too at Horse Gully that an aqueduct at the mouth of the gully would have needed to have been ten times as long at 400 metres as it actually is in the head of the gully.
Sign up to comment.
Sign in if you already did it.
Photo taken in Naseby, New Zealand
Misplaced? Suggest new location