Around 50 vegetable growers from the Waikato and Auckland visited constructed sediment retention ponds (SRPs) at the Hinemoa Cleanfill site in Pukekawa last week. The purpose of the visit was to discuss effective erosion and sediment control measures for cultivated land.
Figure 1: Civil construction sized sediment retention pond.
SRPs are sized to capture runoff from specific catchment areas. At the Hinemoa site, Andrew Barber from Agrilink, along with Chris Nicholson and Jacob Kemp from Hinemoa operations, showcased a civil construction scale SRP capturing runoff from a cleanfill site (Figure 1 below). As a comparison, growers were also shown two smaller ponds designed to capture runoff from ten hectares of cultivated land (one pond draining five hectares is pictured in Figure 2).
Figure 2: One of two sediment retention ponds sized to capture runoff from 10 hectares of cultivated land.
In Pukekohe, vegetables are grown on sloping land, requiring a different management approach than would be used on relatively flat cultivated land, for example, in the Horowhenua. The most common sediment control measure in Horowhenua is a well-constructed and maintained vegetated buffer strip. In Pukekohe, runoff volumes are greater, meaning a buffer strip would not be effective at stopping sediment leaving a paddock, and a more engineered approach like an SRP is required.
During the visit, growers learned that successful sediment retention pond design includes catchment area, volume, shape, decanting device, spillways, forebay and keeping discharged water clean.
A special thank you to Chris Nichols and Hinemoa operations for opening their gates to fellow growers, and sharing their experience in designing, installing and maintaining SRPs.
Following the visit, more than 50 growers attended a Farm Environment Plan (FEP) workshop facilitated by Agrilink. The workshop is part of a series of FEP workshops for vegetable growers offered by Horticulture New Zealand, Vegetables New Zealand, and the Pukekohe Vegetable Growers’ Association.
This workshop focused on mapping and soil management. Agrilink stepped growers through digital property mapping, and soil management using a risk-based assessment approach. Growers need to be able to identify appropriate and time-bound practices in their Environmental Action Plan and keep evidence of completed actions for audit purposes.
A toolbox of erosion and sediment control measures, based on industry research, is available to growers in the Erosion and Sediment Control Guidelines for Vegetable Production.
The next FEP workshop in Pukekohe is scheduled for 2 June, and will focus on nutrient and irrigation management. More information on this workshop will be announced via the HortNZ newsletter.