Skip to content

Future Landscapes

Cascade of Soil Erosion

Developing sediment models to enable land managers, water users, communities and iwi to set sediment-related water quality targets


Challenge funding: $400,000

Research duration: January 2017 – December 2018

What Did We Do?

Soil erosion and too much sediment in rivers can result in major environmental problems. The impact of sediment loads on freshwater attributes such as water clarity, and how this affects freshwater ecology, is not fully understood.

This research has highlighted which sources of sediment have the most important role in determining how much suspended sediment ends up in a river. It has shown that the amount of sediment in rivers with headwaters (first-order catchments) is controlled by the maximum water flow during a storm event.

Cascade of Soil Erosion researchers have developed a model that can be used by regional councils to evaluate the impact of changes to land use and management on the sediment yield of catchments, and help plan soil conservation works.

This modelling will help to target the estimated $120 million expenditure needed to deal with erosion and sediment issues across New Zealand each year.

How Can The Research Be Used?

  • Horizons Regional Council has used this research to assess the impact of soil conservation work in the Manawatū-Wanganui region. The model’s effectiveness was demonstrated by how close its predictions are to actual measurements of sediment loads in the main channel of the Manawatū River. Horizons Regional Council is continuing to implement soil conservation work, and it is predicted that its Sustainable Land Use Initiative will improve water clarity by 30% by 2043.
  • Models developed by this research team can be parameterised with local data, then used in spreadsheet form by regional councils across New Zealand and central government. The models can be used to evaluate the impact of changes to land use and management on the sediment yield of catchments, and help regional councils plan soil conservation work projects of varying size and complexity.
  • Using event-based modelling (based on single storm events), this research project has shed light on the effect of peak water flow on storm sediment load. Further development of this modelling will provide more detail by using rainfall radar information as well as obtaining direct measurements from small successive tributaries during storm events.
  • Our models contribute to the range of tools to evaluate land-use suitability.
  • The Hill Country Erosion Fund was boosted from $8 million to $20 million, enabling more regional councils to use this research.
  • This research has been cited in reports informing the government's 2019 Essential Freshwater proposal, to derive sediment load targets for all catchments in New Zealand, and in the investigation of the practicality of achieving those targets.
  • The models developed by this research team are being further refined in Smarter Targeting of Erosion Control, an MBIE-funded programme (2018–2022).

In the Media

Science omnivore takes on the tough questions

Dairy Farmer, 18 February 2019

A decrease in sediment and phosphorus loads and increase in water clarity was entirely consistent with the predictions in the efficacy of the implementation of farm plans in the Manawatu River catchment.


Community Involvement

  • Cascade of Soil Erosion researchers are working in close collaboration with Horizons Regional Council, who are providing flow and water quality data fundamental to the project. Horizons Regional Council is also sharing data and collaborating in the development and application of event-based sediment loss models for low-order catchments.

Team Snapshot

Research Outputs


An event-based model of soil erosion and sediment transport at the catchment scale

John Dymond, Simon Vale
Geomorphology, October 2018

Soil conservation over large areas is expensive and needs to be targeted to obtain maximum benefit for the least cost. In this paper, an event-based model of soil erosion and sediment transport is outlined in the context of the Manawatū catchment in New Zealand for which all the major tributaries are monitored for water and sediment discharge. Tests demonstrate that the model is robust.

The influence of a flood event on the potential sediment control of baseflow phosphorus concentrations in an intensive agricultural catchment

McDowell RW, Simpson Z, Stenger R, Depree C
Journal of Soil and Sediments, March 2018

We sampled sediments in an agricultural catchment in Reporoa, New Zealand, before and after a scouring flood event. The tributary was chosen for its low slope and predominantly single land use (intensive dairying). This work suggests that despite changes in sediment composition due to flood events, EPC0 is a useful reflection of daytime baseflow-DRP concentrations at sites along a stream network. These data also inform our understanding of the influence of sediment on delaying farm and catchment efforts to decrease in-stream DRP concentrations.

Predicting improved optical water quality in rivers resulting from soil conservation actions on land

John Dymond, Rob Davies-Colley, Andrew Hughes, Christoph Matthaei
Science of the Total Environment, December 2017

Soil conservation not only conserves soil but it improves the water clarity of water in rivers. This improvement may be estimated by the methods shown in this paper. The approach is demonstrated on the Wairua River in Northland, New Zealand. For this river we show that visual clarity would increase relatively by approximately 1.4 times the relative reduction of sediment load. Median visual clarity would increase from 0.75m to 1.25m (making the river more often suitable for swimming) after a sediment load reduction of 50% associated with widespread soil conservation on pastoral land.


SedNetNZ, SLUI and contaminant generation. Part 1: Sediment and water clarity

Les Basher, Raphael Spiekermann, John Dymond, Alex Herzig, Ella Hayman, Anne-Gaelle Ausseil
Manaaki Whenua Landcare Research Contract Report LC3135, April 2018

SedNetNZ, SLUI and contaminant generation. Part 2: Nitrogen, phosphorus and E. coli

Raphael Spiekermann, John Dymond, Andrew Manderson, Les Basher
Manaaki Whenua Landcare Research Contract Report LC3194 for Horizons Regional Council, June 2018

Tool for relating land use/management to sediment rating curve for the Manawatu catchment

John Dymond, Simon Vale
Manaaki Whenua Landcare Research Contract Report LC3397, July 2018


Cascade of Soil Erosion to River Sediment

Simon Vale
Our Land and Water Symposium, April 2017

Have a Question?

We are happy to answer any questions about this research and how it can be used.

Please fill in the form below

Thank you for your enquiry. Your question may require information to be gathered from the research team, so please anticipate that it may take us up to 10 days to prepare a reply.

We appreciate your interest in our research.

  • This field is for validation purposes and should be left unchanged.
Scroll To Top