In this guide, we discuss the main water erosion solutions and control methods available in the market, including their pros and cons.
Water erosion is a natural geological process that has existed since the beginning of time. But, it has become one of the most concerning environmental issues at present, endangering the habitat of humans and other living species. Homeowners, businesses, and governments worldwide are affected by it implicitly or explicitly.
In New Zealand, water erosion is a particularly significant issue due to the country’s steep terrain, high rainfall, and naturally erosion-prone soils. Large areas of hill country, river catchments, and coastal zones are affected by ongoing soil loss, impacting farmland, infrastructure, waterways, and ecosystems. Events such as intense storms and cyclones further accelerate erosion, making effective water management and erosion control strategies essential across many regions of the country.
How has it come to this? When is water erosion a threat? Is your local area or neighbourhood facing this risk at present? If so, what kind of water erosion solutions are effective at mitigating the problem? Let’s talk about it!
What Is Water Erosion?
Water erosion is one of the forms of soil erosion. It refers to the removal of soil and sediment particles from their original location by water, eventually wearing out or “eroding” the land surface. Water can easily wash away loose soil from a place due to the pressure of flowing water or rainy conditions.
Water erosion occurs when rain, runoff, or flowing water dislodges and carries away soil, rock, and surface materials, often leading to the loss of fertile topsoil, changes in landforms, and increased water pollution. Common forms include rainsplash, sheet, rill, gully, and bank erosion, and these processes are frequently intensified by deforestation, overgrazing, and poor land management practices. Effective control relies on maintaining vegetation cover, using terracing, and minimising soil disturbance through reduced tillage.
Water erosion is considered a natural phenomenon, and each soil or land type has its own rate of erosion, which isn’t threatening to the environment around it. However, human activities have accelerated the process of erosion, and have prevented the lands from recovering their quality naturally with time.
Also, climate change, which has contributed to frequent and irregular rainfall and rise in sea level has also increased the risk of water erosion, especially in coastlines. Water erosion control methods play an essential role in mitigating the impacts of erosion.
Bluemont is a leading supplier of innovative water erosion solutions in Australia, New Zealand, and the Pacific Islands.
Different Types of Water Erosion
Water erosion occurs in areas such as creek banks, riverbanks, lake beds, coastlines, etc. We can categorise erosion by water into different types based on how sediments are moved from their original location, which helps us map out appropriate water erosion solutions to mitigate damage. Typically, we categorise it as:
Splash Erosion
This is a direct yet less severe type of erosion caused by the impact of raindrops on the soil. It creates a ‘bombardment effect’, where the force of raindrops causes the soil particles to move in different directions. Depending on the rainfall level, the impact on the soil’s surface can be low or high, destabilising the topsoil layer. If your area is subject to frequent rainfall, the effects of splash erosion can be high.
Sheet Erosion
This type of erosion is a result of water flowing over any sloped area continuously. When the rainfall is constant and forceful, it washes away a uniform layer of soil from the surface. As the entire top layer is wiped out, sheet erosion affects soil strength and quality to a great extent. It can also make the area prone to landslides. This is frequently observed in New Zealand farmland, particularly on sloping pasture where prolonged rainfall causes uniform topsoil loss.
Rill Erosion
Rill erosion causes flowing water to carve out small valleys. When water flows rapidly – cutting deep into the soil – it can wash away soil particles and form small valleys. It is more evident in hills and bare farming fields where the soil tends to be loose. With time, the soil layer depletes and becomes thinner, affecting the quality of the land. In New Zealand, rill erosion is commonly seen in freshly cultivated paddocks and exposed construction sites following heavy rain events.
Gully Erosion
An extreme situation of rill erosion leads to gully erosion. This is a severe type of erosion that makes it difficult to recover the soil structure if we fail to implement adequate water erosion control methods in time.
Flowing water creates wide channels by cutting very deep into the soil. It can even affect the water quality as large amounts of sand get mixed and washed away with water. In this case, basic erosion protection methods may not be enough.
In New Zealand, gully and riverbank erosion are especially widespread in hill country and rural catchments, particularly across regions such as the East Coast, Waikato, and parts of Canterbury. These forms of erosion contribute large sediment loads to rivers and coastal environments, affecting water quality and increasing flood risk.
Why Is It Important to Prevent Water Erosion?
Water erosion can pose many short-term and long-term negative consequences for the environment and the public. However, the impact depends on the severity of erosion.
Primarily, water erosion destabilises and erodes the topmost soil layer. The topsoil layer then finds it difficult to absorb and retain nutrients, losing its quality and impacting flora and fauna. It will affect the growth of crops and other plants in the surrounding area, and the marine animals in the water source will also be affected due to the mix of chemicals in the water. The disruption of the sediment structure due to soil erosion can lead to waterlogging, floods, and increased pollution.
Erosion from water can also threaten the foundation of buildings, properties, and infrastructure. For example, a bridge that runs over a river is at great risk of damage or failure if it’s prone to erosion. This was the case with Gilbert River Bridge and Kholo Creek Bridge, as their bridge pylons had fallen prey to scour. It can disrupt day-to-day activities and threaten human life.
The recent landslide at Mount Maunganui is another example of the devastating impact of mass movement erosion, where saturated soil and rock lost stability and collapsed downslope under the force of gravity.
Triggered by prolonged heavy rainfall, the event resulted in serious safety risks and fatalities, and led to the closure of public access areas. Incidents such as this highlight the need for effective erosion prevention measures, including slope drainage, vegetation reinforcement, geotechnical monitoring, and long-term land stability planning in high-risk areas.
The Accelerating Risk of Coastal Erosion
In coastal areas, a large amount of sand getting washed away can affect the properties and landscape along the line.
New Zealand is experiencing significant and accelerating coastal erosion, with around 40% of its coastline currently affected. Factors such as climate change, rising sea levels, and more frequent storm events are contributing to increasing land loss, particularly in areas like the Coromandel Peninsula, the West Coast, and parts of Auckland, where some locations are projected to lose 15–20 metres of coastline over the next century.
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Erosion Prevention
Coastal, offshore and inland scour remediation
What Are the Solutions to Water Erosion?
Effective erosion control in New Zealand focuses on stabilising soil, particularly on steep pastoral land and during construction, using methods like rock bags, space-planted poplars/willows, afforestation, retaining walls, and riparian fencing. Key solutions include planting native vegetation for long-term stability, installing structural controls like sediment traps, and implementing sustainable land management practices to mitigate damage from high-intensity rainfall. These methods are critical for managing steep terrain, agricultural runoff, and construction site sediment. They also protect productive land, water quality, and infrastructure.
Here are the best methods to prevent erosion by water.
Rock Bags
Our Rock Bags are a simple yet very effective mechanism for controlling water erosion. Also known as erosion bags or rock filter units, they are simply large netted bags containing lots of small rocks. They are increasingly used across New Zealand for coastal protection, riverbank stabilisation, and infrastructure projects.
This innovative Japanese technology prevents water erosion and is applicable for various situations both on land and underwater. The netted bag made from 100% recyclable material is long-lasting and environmentally friendly.
How do erosion bags work?
Rock Bags control wave action and currents while preventing sand from being washed away by water. The soil layer remains covered by Rock Bags and is therefore protected. They slow the water flow and minimise the displacement of soil. They are very versatile in application and can be used to build dams or retaining walls by placing one bag on top of the other.
Rock Bags are ideal for waterway erosion control, coastal and beach erosion prevention, bridge pier scour prevention, offshore erosion control, berth protection, scour protection, and many other applications.
Advantages of Rock Bags
The process of filling and deploying these erosion bags is a simple task, done directly on the eroded site. It requires less manpower, and a single excavator is sufficient for average-sized products. The flexible structure is what makes them unique from other water erosion solutions. You can place them anywhere from river banks to shorelines to slopes to subsea.
The lifespan of the Rock Bags is 50+ years. Plus, they promote the growth of vegetation on land. They also thrive well underwater and are great for seabed erosion. The gaps between small rocks act as a safe habitat for marine life. Over time, you won’t even notice their existence. Another major benefit of erosion bags is they are a cost-efficient choice.
Rock Bags are a better alternative to other water erosion solutions like rip rap because the bag holds the rocks in place. So they won’t be washed away due to water or wave pressure.
Disadvantages of Rock Bags
In all honesty, we still can’t find any cons to this solution! Kudos to sustainable innovation, right?
Gabions
Gabions, gabion baskets, or a gabion retaining wall consist of rectangular boxes of wire mesh filled with materials like small rocks, stones, or concrete pieces. The steel wire mesh of gabions is a construction of double-twisted, hexagonal wire.
How does a gabion retaining wall work?
Gabion boxes can be placed in a row or stacked on top of each other to build a gabion retaining wall. The barrier will stabilise the soil behind and minimise the entry of water. Over time, vegetation can fill the gaps between the rocks inside the mesh baskets and strengthen the structure.
Gabions are one of the common water erosion control methods for sloping areas. In New Zealand, gabions are commonly used in road cuttings, residential developments, and river training works. Similar to erosion bags, you can also deploy them in coastal areas, lakes, river banks and bends, and other waterways to control erosion.
Advantages of gabions
As it’s a simple product of steel baskets containing rocks, gabion erosion control walls also happen to be eco-friendly. The other benefit is that gabions can be assembled and deployed on-site. They are also long-lasting, and their permeability helps drain water easily.
Disadvantages of gabions
Building a gabion erosion control wall is usually expensive and bulky work as they are difficult to install and require large equipment. Moreover, the structure of gabions doesn’t encourage habitat growth all that much. Rock Bags, on the other hand, quickly adapt to the environment and support marine life and plant growth.
Riprap
Riprap is one of the most permanent water erosion solutions. It refers to a layer of rocks or other similar materials of similar size or a mix of different sizes. Rocks vary in size, depending on the location and purpose. If the water pressure is high, you would need heavier and larger rocks to form a solid barrier. This is especially true for coastlines.
How does riprap work?
Similar to Rock Bags, you can use small riprap rocks as ground cover. Here, the rocks act as a filtering layer above the soil to hold it in place during water runoff. You can also build a riprap retaining wall or riprap seawall with large rocks to protect the ground behind the wall.
It is necessary to install a geotextile fabric layer with riprap, especially when providing ground cover for fine-grained soil. It is applicable for steep slopes, riverbanks, beaches, or shorelines for protection against wave action, tides, and high water flow. You can also use this method for bridge pier scour prevention.
Advantages of riprap retaining walls
Riprap seawalls are one of the most traditional solutions for soil erosion in coastal areas as they don’t disrupt access to the sea. As rocks and stones are readily available, building a layer of riprap is easy. It is also a simple mechanism of placing rocks strategically. Selecting sturdy rocks is important – and angular-shaped ones are more effective for this purpose.
Disadvantages of riprap
Riprap is costly in terms of both installation and maintenance. They also give a very cluttered appeal, unlike erosion bags where small rocks are held together in the bag. Without maintenance, the lifespan of a riprap seawall can be short.
It’s also not the most sustainable practice as it doesn’t promote vegetation or support habitat growth. If you need close yet better riprap alternatives, we highly recommend Rock Bags.
Erosion control matting
Erosion control mats are also one of the effective ways to prevent erosion. Also known as soil retention blankets, these are open-weave structures made from biodegradable or synthetic material. Biodegradable erosion control matting usually comes in materials such as straw, coconut fibre, cotton, or jute. Synthetic options usually come in plastics, geo-fibre, or synthetic fibre.
How does erosion control matting work?
Erosion mats hold the soil in place by acting as a protective covering, preventing it from being washed away by water. They are applicable on river banks, lakeshores, beaches, hillsides, and slopes. There are both temporary and permanent water erosion control matting solutions.
Advantages of erosion control matting
The open-weave design of erosion mats allows for plant growth. Biodegradable ones also decay naturally over time, meaning they have no negative impact on the environment. However, it’s not the case with synthetic or semi-synthetic mats.
Drawbacks of erosion control matting
In this case, selecting the right type of mats and installing them correctly is essential. Otherwise, your water erosion prevention project may not be successful. Also, the lifespan of these water erosion solutions is no more than 10 years. They will have to be replaced afterwards. Rocks offer up to 50 years on land with more durability and water-resistant ability.
Disadvantages of concrete mats
Concrete erosion control blocks can also be prone to damage or cracks and are hard to repair. You would have to replace the entire concrete revetment mat as the blocks remain connected. This is why erosion bags are the best. They are extremely durable, and even in unlikely cases of a rip, you only have to replace that particular rock bag.
Tetrapods
Tetrapods are concrete armour units specially engineered to control water erosion. They are a modern design of the conventional rip rap. The term tetra refers to “four,” and “pods” refer to “legs.” Originally, these were four-legged concrete erosion control blocks. However, tetrapods come in different shapes and sizes today – and can weigh anywhere between 3-40 tonnes.
How do tetrapods work?
Tetrapods are a famous coastal erosion solution – just like Rock Bags.
They are mainly used to control wave action and protect coastal structures like seawalls. In New Zealand, tetrapods are primarily used in major port and harbour environments exposed to high-energy coastal conditions.They are interlocked with each other to form a concrete retaining wall. Tetrapods work by allowing water to flow around them instead of against them.
Benefits of tetrapods
The weight and interlocking design of tetrapods work effectively against extreme weather conditions, dissipating the force of the harsh waves. They are a long-lasting and durable option for water erosion control methods.
Disadvantages of tetrapods
While tetrapods are generally stable, the constant exposure to heavy winds and storms can dislodge them from their original place. They can even go into the sea and pose a threat to swimmers. These concrete erosion control blocks also tend to crack with wear and tear. Rock Bags overcome these issues as the netted bag holds the rock together. Not to forget, they also promote plant growth in coastal areas.
Land and Vegetation-Based Erosion Control
Land and vegetation-based erosion control is one of the most common and effective erosion management approaches in New Zealand, particularly across pastoral farmland, hill country, and river catchments. This method focuses on using plants and land management practices to stabilise soil and reduce erosion caused by heavy rainfall and surface runoff, which are major contributors to soil loss in many regions of the country.
How does land and vegetation-based erosion control work?
In New Zealand, vegetation controls erosion by creating a natural reinforcement network within the soil. Deep-rooted plants such as poplars and willows are widely used on erosion-prone slopes, while native species are planted along waterways to stabilise riverbanks and filter sediment. These root systems hold soil particles together, slow water flow, and improve soil structure, significantly reducing the risk of landslides, gully erosion, and riverbank collapse.
Land and vegetation-based methods in New Zealand commonly include space planting poplar and willow poles on hillsides, riparian planting with native species like harakeke (flax), carex grasses, toetoe, and koromiko, fencing off erosion-prone areas from livestock, and retiring unstable land to allow natural regeneration or planned afforestation.
Advantages of land and vegetation-based erosion control
This approach is highly sustainable and environmentally friendly, as it works with New Zealand’s natural landscapes and ecosystems. It improves long-term soil health, enhances biodiversity, and provides durable erosion protection with minimal ongoing maintenance once established. It is also supported by regional councils and national initiatives such as the Hill Country Erosion Programme, making it a widely adopted and cost-effective solution across rural and semi-rural areas.
Disadvantages of land and vegetation-based erosion control
The main limitation of this method is that vegetation requires time to establish before it provides maximum protection. It is less suitable for sites facing immediate or severe erosion risks, particularly in high-energy environments such as exposed coastlines or fast-flowing rivers. In these situations, land-based methods are often combined with engineered solutions like Rock Bags, riprap, or retaining structures to achieve effective erosion control.
In addition to these, there are other water erosion solutions like geotubes for erosion control, strip cropping for slopes, and silt fences. We recommend you consult an expert to determine the best product to tackle the issue in your area.
Wrapping Up
Now that you know how to prevent erosion, you can consider the next steps to mitigating it in your area. Given New Zealand’s terrain, climate, and ongoing coastal and hill country erosion challenges, selecting the right erosion control strategy is essential for protecting land, infrastructure, and ecosystems.
Based on our evaluation, Rock Bags are the best and most effective product available for preventing erosion, which is why we use them for all our water erosion control projects. They adapt well in almost any terrain condition and are one of the most sustainable water erosion control methods compared to others. Plus, they are safe for the environment.
Check specifications and brochures, and get in touch with us to learn more or order Rock Bags for your local project. Bluemont is a wholly-owned Australian company, providing emergency management solutions across Oceania. We have worked on a wide range of erosion control projects in collaboration with local governments and contractors.
You can call us on +64 (9) 872 2622 or email us at info@bluemont.nz. You can also get in touch through our contact page.
Sources:
- https://coastalchange.nz/
- https://niwa.co.nz/news/reducing-sedimentation
- https://www.mpi.govt.nz/forestry/funding-tree-planting-research/hill-country-erosion-programme
- https://www.mpi.govt.nz/dmsdocument/4074-Impacts-of-climate-change-on-erosion-and-erosion-control-methods-A-critical-review-final-report
- https://www.rnz.co.nz/news/national/584886/the-mt-maunganui-tragedy-reminds-us-landslides-are-nz-s-deadliest-natural-hazard
- https://www.nzherald.co.nz/nz/eroding-nz-new-maps-reveal-where-our-coasts-are-crumbling-fastest/OMWZHTQFQZHHPGDDWBBZPICCCE/
- https://www.landcareresearch.co.nz/news/getting-to-the-root-causes-of-soil-erosion-using-high-res-remote-sensing
- https://www.rnz.co.nz/news/national/586651/government-launches-inquiry-into-deadly-mount-maunganui-landslide