Bridge Pier Scour Protection: Alternatives to Riprap and Gabion Retaining Walls

Bridge Pier Scour Protection

Bridges are an integral part of transport infrastructure. They improve transportation and allow us to carry out day-to-day tasks effectively. Without bridges, access to some areas would be pretty much impossible.

If bridges are susceptible to damage, it can hinder a lot of activities, impacting us both economically and socially.  This is why bridge maintenance and protection seriously is no joke and must be taken seriously.

One of the common issues associated with bridges is scouring. If a bridge is at risk of scouring or shows signs of it, implementing bridge pier scour protection measures becomes URGENT

What Is Bridge Pier Scour?

Bridge pier scour refers to the erosion of sediment or soil structure around the bridge foundations. It is a natural phenomenon that occurs due to the impact of fast-flowing water on the river bed.

Piles and piers are two types of foundations that provide support for bridges. A pile is an upright or vertical structure, while a pier is a cylindrical column. Bridge piles or piers interfere with the water flow, increasing its velocity. The obstruction causes the water to flow around them, and the force can wash away the sand gradually. Riprap alternatives for bridge pier scour protection can prevent it.

kyowa rock bags deployed to protect bridge from scour erosion
Stop and prevent the dangers of bridge scour erosion

Why Is Bridge Pier Scour Protection Important?

Bridges that run over waterways are the most vulnerable for pier scour. However, even bridges that run over dry ways such as railways, roads, valleys, and dry creeks can be susceptible to erosion. Heavy rain is enough to cause equal damage if there’s no scour protection. This is where water erosion control methods such as rock bags or a gabion retaining wall come in useful.

Bridge pier scour is a severe problem and is one of the major causes of bridge failure. In the beginning, scour can damage and weaken the foundation, threatening the bridge’s stability. Eventually, if left unattended, it can even lead to collapse.

If a bridge foundation gets damaged, the bridge will likely need to be rebuilt, which is time-consuming, costly for the government, and calls for lots of resources. Still, this scenario can be avoided with the right bridge pier scour protection methods.

What Is the Best Bridge Pier Scour Prevention Method?

If you are looking for a reliable and effective way to stop water erosion and safeguard bridges, we recommend the Kyowa rock bags. Although a simple mechanism, they are a leading bridge pier scour protection solution worldwide. Bluemont is the reputed supplier of Kyowa rock bags in Australia, New Zealand, and the Pacific Islands.

How do rock bags stop water erosion?

A rock bag is a product made of large amounts of small rocks held in a netted bag – made out of 100% recyclable material. Rock filter bags act as a cover for the exposed soil layer and protect them from water runoff. You can place them around bridge piles or piers and strengthen the foundation.

using rock bags instead of gabion retaining wall
Rock bags are a top alternative to riprap and gabion retaining walls

Why rock bags are the best solution

Depending on the size of the pier, rock bags can be placed as a single layer or stacked on top of each other to build a retaining wall. They are very easy to install. You can fill the netted bags at the site and deploy them then and there.

Rock bags are durable and flexible in structure. They also offer a lifespan of up to 50 years. The gaps between rock bags promote vegetation growth, and when submerged, they are a habitat for small fish. This is why it’s one of the best bridge pier scour protection solutions.

Real-world applications of rock bags

Kyowa rock bags were first used to protect the Akashi Bridge in Japan. It was a massive success. They also protect the foundation of London Bridge as a part of its scour mitigation plan.

Over the years, they have been used in numerous bridge erosion control projects. From shielding the Gilbert River Bridge from strong currents to protecting a bridge running over a dry creek from flood damage, these rock bags do a fabulous job.

What Are Other Ways to Stop Water Erosion Around Bridge Piers?

Riprap

Riprap refers to a foundation of rocks, stones, or concrete pieces laid over the soil layer. When placed around bridge foundation structures, the riprap retaining wall will act as a shield and protect the soil from getting washed away by water runoff.

Riprap is more expensive than some other bridge pier scour protection measures and requires constant maintenance. This is why many look for better riprap alternatives.

Challenges of using riprap

It is important to select rocks of the right size and angularity for the construction of a strong rip rap retaining wall. Only then it will battle against the force of water effectively. For faster currents, we have to choose large rocks. For slower currents, small to medium-sized rocks are required.

If there’s no filtering layer beneath, it poses the problem of leaching too. It is one of the main disadvantages of riprap. 

Also, as there’s nothing that holds the rock together, water pressure can wash them away as well. It is the same case with a riprap seawall. Then, it won’t stop water erosion effectively. In this regard, rock bags are the best riprap alternative because the rocks are inside a netted bag.

Gabion retaining walls

Gabions are another bridge pier scour protection method. They are wire mesh boxes filled with stone, rocks, or concrete. Construction of a retaining wall around bridge piers using gabion boxes provides resistance against scour. It will stabilise the soil layer around bridge piers by acting as a barricade.

Challenges of using a gabion retaining wall

The gabion erosion control method comes with a set of drawbacks. If the gabion boxes are stacked one on top of another, a strong lateral force can cause them to collapse without a sturdy wire intertwining them together. They don’t promote vegetation – unlike rock bags that are eco-friendlier and sustainable.

It is not easy to install a gabion retaining wall as you need space to prepare the wire mesh baskets on the site and deploy them. On the contrary, we can prepare and deploy Kyowa rock bags even in a small area. That’s why protecting Kholo Creek Bridge from erosion was a no-brainer!

A gabion retaining wall is also very difficult to maintain, and if there’s damage in one cage, the entire wall has to be disassembled.

If you would like to find out more about how the Kyowa rock bags stop bridge scour, or are working on a project in your area, call +61 2 9091 0360. You can also email us at  [email protected] or fill in our contact form.

We are Australia’s leaders in erosion and emergency control solutions, providing protective systems and solutions across Oceania for the past 18 years. 

In the meantime, learn more about the Kyowa rock bags, here: