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The ‘contributor’ principle is a relatively new concept introduced by both the RPA and the LGAA. The contributor principle is used to assess the degree to which the characteristics or use of the land, or the actions of the occupiers of that land contribute to the need for flood protection, river management and soil conservation works and services.

The physical characteristics of properties, and the past and present actions of the occupiers both affect maintenance costs. In the past, occupiers have assumed they have had a right to discharge water from their properties. The amount of water being discharged is increasing as a result of continued pastoral development and drainage improvements.

Water discharge has occurred not only on the flat areas of the greater Waikato catchment, but also in rolling and steeper districts where shallow gullies and swampy flats have been drained. Over recent years, the expansion of intensive livestock farming into steeper areas has been one of several factors driving this continued trend.

Justice Morris, in respect of the Piako River Differential Rating System, in ‘Brockelsby and Others v Waikato Regional Council (2001)’ stated, “I find it unreal to say the higher properties do not receive some benefit, albeit minimal, from the proposed drainage scheme. Clearly they do on the material before me. The common law right to discharge water from the higher ground still exists but the ability of a scheme to move any water so discharged away from the lower land more quickly must benefit the higher land in turn enabling water falling on such land to flow faster from it thus lessening the risk of ponding and the like.”

Ratepayers in hill country areas are assessed as being liable for Project Watershed rates both as beneficiaries and contributors. As beneficiaries, they experience the same indirect benefits as others in the lower areas of the catchment and which have been attributed to all ratepayers through the general rate and the catchment and zone differentials. These indirect benefits include public safety, security of transport links and reduced inconvenience, recreational benefits, aesthetic benefits and secondary economic benefits arising from the wider range of land use options Project Watershed assets provide.

In addition to receiving benefits (either direct, indirect or both) properties throughout the greater Waikato catchment are also liable as contributors. This is generally because the development of these properties to pasture and the continuation of this land use has increased the ‘speed’ with which water runs off these properties, increasing the peak flows in streams and rivers further down the catchment. This affects flooding and erosion, requiring higher floodbanks and increased pumping head.

The contributor assessment is based on comparing the current land use to the ‘natural’ state of the catchment. The development of land to its current use has led to changes in soil erosion and runoff characteristics. Other activities also affect the erosion and runoff characteristics of the catchment and river system.

Mean annual flood peaks from catchments that are developed to grazed pasture have increased flows by 60 percent, compared with a native bush land use. Land in urban, industrial, commercial or roading increases the stormwater runoff significantly over that from pasture or bush/forest, due to the proportion of impervious surfaces.

In assessing what the ‘natural’ state of the catchment was, reference was made to a number of information sources.

For the purposes of applying the contributor assessment for the funding system, a broad comparison of current land uses and activities has been carried out in relation to the ‘natural’ or benchmark land use, including native forest, wetland and tussock. Plantation forest is also assumed to have similar hydrological characteristics to native forest.

Council has considered that costs should be allocated to ‘contributors’ on the following premises:

• That development of the greater Waikato catchment through land clearance, land drainage improvements, river and drainage system development and urban development has increased peak river flows. (A substantial body of scientific research, engineering knowledge and practical experience backs this up).
• That the assessment of contribution should be based on the difference between the natural conditions and the modified (current) conditions.
• That the increased flows have increased the cost of ongoing maintenance of the existing schemes.

Council has obtained independent technical advice on the contributor effect on the different components of Project Watershed. The principal contributor effects are:

• Flooding - The peak rate of flow down a river will determine the level of inundation of land immediately adjacent. Changing land uses can affect the peak flow. Generally the more intensive the land use, the greater the rate of runoff. The velocity of the flow that floods land is directly related to the damage to the land itself, fences and buildings.

 

• Drainage - Drainage outfall from a property will be affected in some manner by the water levels in natural watercourses. Where there are increased flows in drains or rivers, the outfall is impeded.

 

• Peat land - Before it was drained for settlement, much of the peat land in the catchment was periodically flooded from the main rivers. These peat areas provided a natural storage zone for floodwaters, lowering the flood peak and then gradually releasing the floodwaters over days and weeks.

 

• Sedimentation and degradation - Hydroelectric dams trap sediment and reduce the natural sediment being transported through the river system. The loss of the natural sediment can lead to instability in the banks and bed of the river system and as a result, bank stabilisation measures may be required.

 

• Channel stability - There are fluctuations in river flows through hydroelectric generation or gate controls. This can increase bank slumping and on-going erosion because there is no natural settling down period before another ’flood’ removes further material.

 

• Increased flows through land use changes and hydro diversion from out-of-catchment.

 

• Soil erosion - Soil erosion is affected by many factors, including geology, soil type, slope, aspect, rainfall events, vegetative cover, grazing intensity, cultivation and others. It is reasonable to generalise that increased erosion can be caused by loss of adequate vegetative cover, loss of soil structure through reduced organic matter in the soil profile, rapid changes in groundwater levels and increased runoff from land use changes.