Case Study: Wetland Project in Thimphu, Bhutan

Introduction

For a wetland restoration project in Thimphu, Bhutan, Ocean Non Wovens laid and welded 19,125 square meters of 1.5 mm HDPE liner and laid 36,540 square meters of geotextile. The liner holds water in the wetland; the geotextile protects the liner, controls erosion and supports planting.

Wetlands filter water, absorb flood flows and provide habitat. A degraded wetland loses water through its bed and banks, so restoring it means holding water at the right level and keeping soil in place long enough for vegetation to re-establish. Ocean Non Wovens manufactures and supplies geosynthetics.

Project overview

The project restored a degraded wetland area in Thimphu to improve its ecological function and biodiversity. Geosynthetics were used to manage water levels, prevent soil erosion and support vegetation growth. Ocean Non Wovens carried out two scopes:

• Ocean Laying & Welding of HDPE liner 1.5mm
• Ocean Laying of Geotextile

The quantities were 19,125 square meters of HDPE liner and 36,540 square meters of geotextile.

Thimphu sits at about 2,300 m in the Wang Chhu valley. Most of its rain falls in the summer monsoon, and winters are cold, so a liner here goes through large seasonal swings in temperature and water level.

Product details

HDPE liner 1.5mm

High density polyethylene (HDPE) liners are used in environmental and civil engineering work for their durability, chemical resistance and very low permeability. In the wetland, the 1.5 mm HDPE liner provided:

• Water containment: it holds water in the wetland at the intended level and stops it draining into the ground beneath.
• Chemical resistance: HDPE resists a wide range of chemicals, which protects the liner from deterioration if contaminated runoff enters the wetland.
• UV resistance: carbon black in the sheet protects it where it is exposed to strong high-altitude sunlight, although covering the liner with soil or water extends its life further.

The welding was carried out carefully. Field seams are the most common source of leaks in any geomembrane, so HDPE panels are normally joined by hot wedge welding for long seams and extrusion welding for details, with seams tested before the liner is covered.

Geotextile

Geotextiles are permeable fabrics used with soil to improve its behaviour. In the wetland, the geotextile supplied by Ocean Non Wovens provided:

• Soil stabilisation: it held soil in place against erosion and gave vegetation a stable base.
• Filtration: water passes through while soil particles are retained, preserving the wetland’s natural filtration.
• Vegetation support: by holding soil around root systems, it helped wetland plants establish.

In lined water bodies, a non-woven geotextile is also commonly placed under and over the geomembrane as a cushion, protecting it from puncture by stones in the subgrade and in the soil cover placed on top.

Implementation and challenges

Installation

Installing the HDPE liner and geotextile required careful planning. The team dealt with:

• Terrain: the wetland’s uneven ground required precise liner placement to contain water effectively.
• Weather: heavy rain interrupted installation. Welding needs a dry, clean sheet, so the team adapted the work to finish on time without compromising quality.
• Environmental care: disturbance to the existing ecosystem was kept to a minimum, with work carried out to limit disruption to local plants and wildlife.

How the challenges were handled

• Technical support: Ocean Non Wovens’ technical team guided the installation throughout.
• Material quality: the HDPE liner and geotextile performed reliably in difficult site conditions.
• Collaboration: working closely with local authorities and environmental specialists addressed ecological concerns and kept the project in line with environmental regulations.

Impact on the wetland

• Water management: the HDPE liner contained water and maintained the levels the wetland ecosystem needs.
• Erosion control: the geotextile stabilised the soil, reducing erosion and sedimentation.
• Biodiversity: the improved conditions supported native vegetation and provided habitat for wildlife.

About Ocean Non Wovens

Ocean Non Wovens supplies and installs geomembranes and geotextiles for environmental and civil engineering projects. Contact the team to discuss a project, or see more case studies, including the pond liner range.