Discussing the new sediment pond are (from left) Pourakino
Valley farmer Dave Diprose, Fish and Game Southland officer
Zane Moss and Environment Southland's David Moate. Photo by
Last summer, Pourakino Valley farmer Dave Diprose noticed
that the duck pond he created in 2009 was rapidly filling with
''I was shocked at the amount [of] sediment there was and how
much soil I was losing from my farm,'' Mr Diprose said.
''I am also concerned about the damaging impacts sediments
and nutrients are having on the Pourakino River and the
Jacobs Estuary at Riverton.''
Determined to reduce the amount of soil and nutrients lost
from his farm, as well as the negative impacts to the
environment, Mr Diprose contacted Fish and Game Southland and
Environment Southland to measure and analyse the sediment
material and design a new pond to more effectively capture
the sediment and nutrients before entering the Pourakino
Environment Southland's land sustainability officer David
Moate said they knew those types of ponds collected sediment
and there was lots of information around on sediment in
waterways, but they had never measured it on a farm pond
''With the naked eye there was a lot, and then we measured it
and we were even more surprised,'' Mr Moate said.
Environment Southland aquatic scientist Dr Andy Hicks led the
sampling investigation into Mr Diprose's pond.
The results showed that the sediment load in the 10m by 30m
duck pond was found to have 118cu m of slurry containing 37.7
tonnes of sediment, 3.3 tonnes of carbon, 201.5kg of nitrogen
(N) and 47.8kg of Phosphorous (P).
This material has come off a 23.31ha catchment that has been
farmed in a normal manner and has not been used for intensive
winter crop grazing.
The small waterway flowing into the pond is highly modified
and mostly tiled, with only a short open section that is
fenced with good riparian vegetation cover.
The recovered sediment contained nearly $600 worth of
fertiliser, which Mr Diprose plans to reapply to his
The pond cost about $550 to construct so has paid for itself
in only four years.
Prior to the pond construction the 100m of open drain below
the pond site required regular cleaning.
With the pond collecting the sediment, this drain has not
needed cleaning in four years and is unlikely to need
cleaning for several more years adding to the savings Mr
Diprose is making.
While the pond has trapped most of the coarse sediment, much
of the really fine sediments were still being lost and given
these are the particles containing most of the P, Mr Diprose
decided to extend and reshape the existing pond to recover
''I needed a sediment trap that was easy to construct and
maintain without taking up too much land and I'm very happy
with the results,'' he said.
''The advice and assistance I received from Environment
Southland and Fish and Game in planning these ponds has been
great, and I'd encourage other farmers to contact these
The new sediment trap pond design is a combination of Niwa
science and on-farm practicality with a little bit of duck
Construction was completed in April this year and cost $2325.
It consists of two separate ponds joined by a culvert pipe,
with the outlet joining an open drain going around the ponds
and back into the field tile.
The two ponds have full digger access for easy removal or
storage of the accumulated sediment.
This material can be directly returned to the paddocks using
a muck spreader or allowed to drain and then moved with a
Southland Fish and Game operations manager Zane Moss said it
was great to be contacted by Dave, to look over his farm and
discuss his concerns.
''Dave was aware of the sedimentation issues in Southland's
estuaries and was keen to ensure he did his bit to minimise
any potential losses from his own operation and he should be
commended for the steps he's taken,'' Mr Moss said.
Mr Moate said the sedimentation of our streams, rivers and
estuaries was a real concern as it was highly damaging for
the health of these ecosystems.
''There's no one area where it's coming from and all sectors
will have to do their bit to help.
''The great thing about the work we've done with Dave is that
it shows it's actually cost-effective to form these sorts of
ponds,'' he said.
David and Joanna Diprose were recently recognised with a
highly commended award for the innovation put into their
sediment trap at the Southland Environment and Conservation
- David Moate