SSI Environmental · Spill, Silt & Environmental Protection · Ireland

What Are the Solutions to Siltation? Sediment Control Methods Explained

Quick Answer

The main solutions to siltation on construction sites are: (1) silt fence (Terrastop) to intercept surface runoff, (2) silt sumps or settlement chambers to allow suspended sediment to settle before discharge, (3) settlement ponds for large volume runoff on major sites, (4) coir or straw erosion blankets to stabilise exposed slopes, (5) check dams in drainage channels, and (6) flocculants for high turbidity water where passive settlement is insufficient. In Ireland, the EPA Construction Guidelines and Inland Fisheries Ireland (IFI) enforcement make documented sediment control a legal requirement on all sites disturbing over 0.5 ha.

Siltation is one of the most common environmental compliance risks on Irish construction sites, and controlling it requires more than a single product. This guide sets out the six sediment control methods used on Irish sites and explains where each is best applied.

The Six Solutions to Siltation

• 1
  Silt Fence Silt fence is the most widely deployed sediment control measure on Irish construction sites. It consists of a woven geotextile fabric stapled to wooden or metal stakes and installed across drainage paths and along site perimeters. Runoff flows against the fence and passes through the geotextile, which retains suspended sediment particles. The fence is effective at controlling fine silt and clay in surface runoff from areas of disturbed ground.

  Silt fence is best used as a perimeter or intermediate measure, controlling dispersed, shallow overland flow, but it will be overwhelmed by channelled flows or heavy rainfall on large drainage areas. On Irish sites, SSI Environmental supplies the Terrastop silt fence system, a specification grade UV stabilised product designed for the extended service life typical of multi year Irish civil engineering projects.

• 2
  Silt Sumps and Settlement Chambers A silt sump is a chamber or contained area where turbid runoff is held temporarily, allowing suspended silt particles to settle under gravity before the clearer water above is discharged. Silt sumps are used where silt fence alone is insufficient, on sites with large impervious areas, high rainfall events, or where silt concentrations in runoff are too high for permeation based controls.

  SSI Environmental's patented, award winning Silt Sump is an Irish developed deployable system that brings sump technology to construction sites quickly and without the need for purpose built infrastructure. It has been deployed on hundreds of Irish construction projects, including road schemes, windfarms, and river works, and represents the most practical siltation solution for medium to large Irish sites where rapid deployment and demonstrable compliance are required.

• 3
  Settlement Ponds For large sites, motorway contracts, major infrastructure, large housing developments, a purpose built settlement pond is often specified by the engineer. A settlement pond is an excavated basin lined with an impermeable membrane, sized to retain a significant proportion of site runoff and allow sediment to settle before controlled discharge. Settlement ponds require more lead time and ground than a silt sump, but can handle very large volumes and can be equipped with controlled outfalls with penstock gates to manage discharge timing.
• 4
  Erosion Blankets (Coir and Straw) Erosion blankets are placed directly on exposed soil surfaces, slopes, embankments, topsoil stockpiles, newly seeded areas, to protect against rainfall impact and surface runoff erosion. By reducing the energy of rainfall hitting bare soil, they dramatically reduce the amount of sediment generated in the first place, which makes all downstream controls more effective.

  Coir blankets (woven coconut fibre) are the most durable option and are used where vegetation establishment takes 12 to 24 months. They biodegrade naturally once vegetation is established, eliminating the need for removal. Straw blankets are a lower cost option for gentle slopes and short durations.

• 5
  Check Dams Check dams are small barriers installed across drainage channels and swales to reduce flow velocity and allow suspended sediment to settle out. They are typically constructed from straw wattles, rock gabions, or purpose made geosynthetic barriers placed at intervals down the channel. Check dams are effective when sediment laden water is already in a defined channel and needs to be slowed before reaching a silt sump, settlement pond, or watercourse.
• 6
  Flocculants In high turbidity situations, particularly where fine clays remain in suspension long after other measures have been applied, flocculants can be used to chemically coagulate suspended particles so they settle faster. On Irish sites, the most commonly used flocculants are polyacrylamide (PAM) gels and chitosan based products. Flocculant use requires careful dosing and must be approved; incorrect application can itself create a pollution risk. Flocculants are a treatment of last resort and should be combined with other passive controls, not used as a standalone measure.

Sediment Control Methods: Quick Comparison

What Is the Purpose of Silt in Construction?

Silt and fine soil particles are a natural constituent of earthwork material. They are not inherently harmful in the ground. The problem arises when construction earthworks disturb bound soil, exposing fine particles to rainfall. Rain detaches the fine particles from the soil surface, runoff carries them to drains and watercourses, and there they cause harm by raising turbidity, reducing dissolved oxygen, and smothering aquatic habitats.

The purpose of sediment control in construction is therefore to replicate the binding and filtering function that undisturbed vegetation and topsoil normally provide, keeping the mobilised particles on the site, not in the water. Any incident that allows silt laden runoff to reach a watercourse can be enforced against by Inland Fisheries Ireland, which is the state body responsible for protecting Ireland's fish stocks and water quality under the Fisheries Acts.

Frequently Asked Questions

• What are the solutions to siltation on a construction site?

  The primary solutions are silt fence for perimeter control, silt sumps for active runoff management, settlement ponds for large sites, erosion blankets for slope protection, check dams for drainage channels, and flocculants for high turbidity events. In Ireland, a combination of silt fence and a deployable silt sump (such as the SSI Silt Sump) is the most common practical approach for sites from 0.5 to 10 ha.
• What is the best sediment control for a wet Irish climate?

  Ireland's high rainfall intensity means passive silt fences alone are often overwhelmed during heavy rainfall events. The most effective approach combines perimeter silt fence (Terrastop) with an active silt sump to manage the volumes that bypass or overtop the fence during intense rainfall. Coir blankets on all exposed slopes reduce sediment generation before it reaches runoff controls.
• Are silt fences required by Irish law?

  Irish law does not prescribe specific sediment control measures by type. However, EPA Construction Guidelines require an erosion and sediment control plan (ESCP) for sites disturbing more than 0.5 ha, and IFI can prosecute under the Water Pollution Acts for any silt incident that reaches a watercourse. Silt fence is the most commonly specified ESCP measure and is referenced in EPA guidance as a required control.
• How long does a silt sump take to deploy?

  The SSI Silt Sump can typically be deployed and operational within hours of delivery. It does not require excavation, concrete, or specialist plant, it is a deployable system that can be positioned wherever turbid runoff is concentrating on site. This makes it particularly valuable at the start of projects, before more permanent earthwork settlement measures are constructed.