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Re-Vegetation Research Project at Duck Creek Farm Report 4

Client: Auckland Regional Council

Date:  2 June 2006

Brief:   To establish and to evaluate a protective vegetation cover on disturbed sites by means of hydromulching

Report number 4 on the results of re-vegetation by means of hydromulching at Duck Creek Farm

The site
A northerly facing cut face of an angle exceeding 45 degrees approximately 90 x 2.5 metres. Due to the northerly aspect and the steep angle of the slope the site tends to remain dry even during periods of high precipitation.

Date seeded
1 June 2006

Evaluation of the site on the 16 October 2006

Observations made
During the four weeks following the last inspection the site received frequent and adequate precipitation. Although there had been good precipitation on the days prior to the inspection most of the upper section of the bank was found to still be very dry.
On the steepest driest sections of the slope there has been further massive mechanical failure where whole sections of the upper the bank have become dislodged. It has become very clear that exceeding the angle of repose on these sections is responsible for the collapse of the upper portions of the bank. This can be clearly seen in the accompanying photographs.

On inspection of the site it was found that good growth has continued on the lower two thirds to three quarters of the slope. There has been poor or no germination of the seed applied, most of which still remains glued to the slope in a band along most of the upper slope in the root zone of the vegetation growing above..

The more northwest facing sections of the site have as expected continued to shown inferior results. A fair amount of germination of the other seeds applied has occurred in particular flax. In some areas bent and other grasses with a creeping habit have crept down the slope from the top.

300 g of Nitrophoska 12% N, 10% P, 10%K, 4.6 % Ca, 1.2 % Mg fertilizer was distributed over the entire area that was seeded.

In conclusion
The results are satisfactory although not as good as expected. This is due to a number of factors. Firstly the slope is too steep for the soil type, which quickly dries out and becomes crumbly. This caused it to become unstable and to collapse before the vegetation could develop a deep enough root system to give it some support. The soil type and structure also prevented moisture from penetrating deep into the soil, causing the slope to dry out rapidly. Even immediately after periods of heavy rain most of the slope remained fairly dry. The dense band of vegetation that has been established at the base of the bank is acting as an effective filter in preventing soil that is becoming dislodged from the bank from washing off of the site into the water coarse below.

The fertility levels should be kept at a level that ensure continued healthy growth so as to continue the natural heeling process that has been initiated, stock should be kept off of this area for as long as is possible to help continue this process.

Recommendations for future sites
The mechanical failure of the slope that has been encountered, which contributed to a partial failure of the seeding operation could be avoided in future if the slopes can be kept a little more moderate in particular where the soils have a texture and structure, which causes them to crumble when they dry out.
As most damage occurred on the upper quarter of the slope a further reduction of the angle of the slope in this area would greatly help prevent the problem of mechanical failure of the slope. This reduction in the slope angle would also greatly increase the moisture available to the seeds both for germination as well as their continued growth, in addition it reduces competition between the establishing and established vegetation above. This would go a long way towards preventing the poor development in these areas as encountered on this test site.
From the valuable experience gained at this site I recommend that further work of this nature implement my recommendations above and that the hydroseeding be carried out shortly before the first rains are expected in the autumn to obtain the best results.

Michael Hickman

duck creek
duck creek  

duck creek

duck creek

duck creek

duck creek
jMichael Hickman Dip. Parks & Recreation Admin. Cert. Hort. Cert. Turf Management

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