Proposed Muggeridges pumpstation – drainage management plan
Report: TR 2015/18
Author: Hajari Thakur
The proposed Muggeridges pumpstation is an important capital works project within the Pouarua area of Piako River Scheme (PRS). The purpose of the pumpstation is to provide and maintain a continued drainage service to the current PRS standard for the community and farmland in the Muggeridge area.
The area of land bounded by Kaihere Road to the East and South, Pouarua Road to the West and Orchard Road to the North is experiencing poor drainage and ponding, due to ongoing peat settlement. This area is a part of Pouarua Peat Dome which has been developed over many years into pastoral farming. This change in land use has resulted in steady rate of peat settlement, and the drainage system has been progressively modified to suit the changed land contour to provide ongoing drainage to the area.
A number of pumpstations (Phillips Road, Torehape, Stitchbury’s and Kaihere) and floodgates (Philips Road, Muggeridges, Torehape, Stitchbury’s and Kaihere) were installed along Piako River in the area (generally in the 1960’s and earlier) through the Piako River Scheme, to provide drainage services for existing farmland. Refer to Figure 1 for Muggeridges catchment and locations of the pumpstations.
As the peat soil within the Muggeridge area has consolidated, resulting in land contour changes overtime, this drainage service is now becoming compromised. Peat settlement has resulted in land within the Muggeridge area now approaching mean sea level (MSL) in some parts, and the present scheme floodgate and pump outlets are becoming ineffective for this area. This peat settlement will continue until underlying clay levels are reached in approximately 100 years, with land levels expected to be around 1.5metres below MSL at that time.
The Muggeridges pump is to provide drainage to the specific area which is currently poorly drained and experiencing ponding, and the expectation that peat consolidation will continue to compound this issue, and eventually result in complete failure and loss of this farm land. As well as avoiding future degradation of this productive farmland, the operation of the pumpstation will maintain the productivity of the land, maintaining economic activity in the area and contribute to the overall productivity of the Waikato Region. The Muggeridge pumpstation would replace the existing scheme outlets currently servicing this area.
The Muggeridges catchment was initially conceived as a part of Pouarua catchment. However further investigations, the pattern of drainage and peat settlement indicates that the low lying Muggeridges catchment is currently largely separate from the Pouarua catchment, and can be totally isolated from the Pouarua catchment. This would both provide optimisation of the drainage network, and protection of the adjacent Torehape wetland from drainage within the Muggeridge area.
The purpose of this report is to set out a drainage plan for the development and management of the Muggeridges area, with the aim of achieving both:
- Maintenance and optimisation of drainage and farm productivity
- Minimisation of adverse effects, including protection of the Torehape wetland and minimising rate of peat settlement.
The report includes:
- An outline of expected peat settlement and land changes over the next 100 years
- Infrastructure and drainage network changes, required to maintain land productivity and service levels, and adapt to changing land levels over time
- Management actions and practices required to ensure isolation of the Muggeridges area from Torehape wetland, and to minimise other potential adverse affects
- Roles and responsibilities
This report provides an overall view of the current drainage system and drainage issues and failures in the Muggeridges catchment and also highlights the future drainage problems due to peat settlement if the proposed pumpstation is not installed, and provides a layout for the changes required in the drainage system to sustain the impact of land settlement in future.
|2.2||Pouarua catchment surface hydrology||3|
|2.3||Ground and clay levels||4|
|2.4||Catchment areas adjacent the Muggeridges catchment||5|
|2.5||Benefits from the Muggeridges pumpstation and the associated works||6|
|3.2||Peat settlement rate||7|
|3.3||Projected land contour||8|
|3.3.1||Projected land contour for 2037(25years)||8|
|3.3.2||Projected land contour for 2062(50years)||9|
|3.3.3||Projected land contour for 2112(100years)||9|
|4||Muggeridges pumpstation and catchment plan||10|
|4.1||Muggeridges catchment plan||10|
|4.3||Proposed pumpstation design||11|
|4.3.1||Sizing of pumps||11|
|4.3.3||Design flood level||12|
|4.4||Inlet canal sizing and staging||12|
|4.5||Drainage network design and management||12|
|4.6.1||Torehape/ Pouarua separation||14|
|4.6.2||Local pump catchments||15|
|7||Management and monitoring plan||19|
|7.1||Roles and responsibilities||19|
|7.2.4||Land use management||20|
|7.2.6||Land change monitoring||20|