Should we graze our DCC water catchment area?


From: Lee Vandervis <>
Date: Thursday, 28 November 2019 at 10:32 PM
To: Peter Foster <>, “” <>, <>, Andrew Whiley <>, <>, <>, <>, Jim O’Malley <>, <>, <>, <>, <>, <>, <>
Cc: Tom Dyer <>, Robert West <>, Simon Drew <>, Sue Bidrose <>, Sandy Graham <>
Subject: Re: Burnt Catchment area

Thank you for your wildfire information and suggestions as below Peter.

Another similar wildfire graph comes from the US :

Screen Shot 2019-11-28 at 10.22.18 PM.png

The issue of grazing the water-catchment area is one that I hope DCC staff will have a considered look at again, as a win/win seems likely to be available as you suggest.

Kind regards,

Cr. Lee Vandervis

47 Garfield Avenue
Dunedin 9010

From: Peter Foster <>
Date: Thursday, 28 November 2019 at 1:39 AM
To: “” <>, <>, Andrew Whiley <>, <>, <>, <>, Jim O’Malley <>, <>, Lee Vandervis <>, <>, <>, <>, <>, <>
Subject: Burnt Catchment area


Greetings Councillors,

When I spoke at the last DCC public forum last month, Councillor Vandervis asked about grazing animals in the water catchment area to reduce fuel load. The answer was a clear yes and here below is a graph from Western Australia that shows the effect of prior burning on the incidence of wildfires.

Screen Shot 2019-11-28 at 10.40.02 PM.png


The second question was related to the issue of animal faeces polluting the water being collected for Dunedin City.

Before answering this in more detail let me say that several decades ago I was a research biochemist who grew cultures of E coli every week so I know bacteria, As a part geologist I understand sedimentation processes and as a farmer of 40 + years I have observed first hand what happens to animal faeces.


Your DCC water manager was in the ODT last week flatly ruling out grazing animals in the water catchment. This is an emotional response, not a considered one.


Firstly, your catchment is already occupied by many animal species, rabbits, opossums, hares, mice, rats, fish, lizards ducks and other birds, all of whom are living defecating and dying in the catchment. So, no way is this catchment  free of the effects of animals.


Secondly, faeces do not get washed into rivers by every passing shower, the land would have to be very steep and the rain very heavy to wash faeces into the waterways. Faeces lie where they are dropped and break down over a period of a month or two providing fertilizer for nearby plants. The soil and the organisms that live in the soil are very good at removing any contaminating material. Coliform bacteria in faeces grow best at body temperature and will not compete for food with the billions of natural soil bacteria whose optimal temperature is usually around 15 degrees.


  1. If the area is not grazed then the grass grows in spring summer, dies off into the winter and becomes a fuel load heading into the next spring. Decomposition of dead grass at the bottom of the pile will produce CO2, methane and nitrates (nitrogen in the grass is first broken down to ammonia and then it is used by bacteria that convert it to nitrate) Ammoniacal compounds and nitrates are extremely soluble and will dissolve in rain water.


  1. The obvious animal to graze would be sheep as they mainly produce small dry faeces, they do not like water other than to drink, they do not wallow or wade in it as cattle do.


5, The aim of the exercise is to reduce the fuel load, grazing the area from spring through to autumn and removing them for winter would have the desired effect without having animals pugging ground during the winter. This could be bonus for adjacent farmers, an income stream for the DCC and reduce the fuel load to the benefit of the catchment. A win win for all concerned.


Checking contamination.

I would suggest testing water from both catchment creeks and nearby creeks that drain adjacent farmland. I strongly suspect that there will be little difference in bacterial count or  chemical content.  All water contains bacteria, it is only the type and concentration that determines whether it is safe or unsafe to drink. Waterways are very good at self cleansing  and grass is very good at trapping sediments.


Given that you already have a significant animal population in the catchment I very much doubt that adding grazing animals from September to March will make any detectable difference. Testing your catchment water now and adjacent farm creeks should provide the information necessary to be assured that this is a safe process.


I am on the committee of East Otago Rivers catchment group and it is our intention to do such testing in our area as the draconian government measure blame farmers for un swimmable rivers, yet data to date show rural river are all swimmable, the pollution that makes rivers unswimmable comes from towns and cities.

eg check out the bacterial counts on Leith, Kaikorai rivers and Thomsons creek below Omakau and compare them with purely rural waterways.



Peter Foster
61 Whites Rd
R.D. 1
Waikouaiti 9471

Mobile – 0272657885

This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s