Landscaping on Colombo-Katunayake Expressway, enchanting

by Henry Rajapakse

Many like to drive along a road planted with flowering and shady trees interspersed with ornamental shrubs. Ideally, every road should be of aesthetic value. By location and design, a road should be a pleasure to drive on. Trees are objects of continuous pleasure. They provide a restful effect and a riot of natural colours during the flowering season. Another important advantage of planting trees along a highway is to concentrate the attention of the driver on driving safely without diverting his sight from the path.

The median strip of the CKE beautified with Cristin plants

Plants under the Katunayake overpass

Bougainvillea plants along the Katunayake overpass

Turfing embankments encircled by concrete rings

When you enter the Colombo-Katunayake Expressway (CKE), the beautiful surroundings invite you to an open landscape in a different world. Unlike Sri Lanka's other highways, the CKE takes you through different landscape sceneries within a short time, but you must not divert your attention from the highway as you are driving at 100 km per hour.

The first part of the CKE is laid through the Muthurajawela wetland, which harbours moisture-loving plants and mangrove trees. In this part of the Expressway, the ground water level is so high that it had to be taken in to careful consideration when selecting planting material. The last part of the highway near Katunayake is laid out bordering the lagoon, hence the trees selected for this area had to be sea breeze tolerant.

When selecting the appropriate trees to be planted along the CKE, the international rules of highway tree planting schemes were followed as much as possible. The tree species selected should be able to adapt to the high moisture condition in the soil.

The trees should especially resist the moist condition of the soil. Trees should be hardy, long lasting and medium in size. They should have a good growing habit and without frequent falling leaves, twigs and branches. They should possess a deep root system for good anchorage.

These trees should be symmetrical, with straight stems, without low branches and with crowns that are not too open or too compact.

Some of the moisture-loving trees planted along the highway are Lagerstroemia speciosa (Murutha), Barringtonia asiatica (Mudilla), Barringtonia racemosa (Diya Midella), Ochrosia oppositifolia (Wel Kaduru), Thespesia populnea (Gansooriya), Pisonia grandis (Wathabanga) Syzygium cumini (Madan) and Ardisia willisii (Lunu Dan).

Where the water level is considerably below the soil surface, trees such as Cassia fistula (Ehela), Peltophorum peterocarpum (Kaha Mara), Delonix regia (Mei Mara), Pongamia pinnata (Karanda), Syzygium rubicundum (Karaw), Bauhina purpurea (Koboneela), Mimusops elengi (Muna Mal), Mischodon zeylanicus (Thammenna) and Mitragyna tubulosa (Helamba) were planted. Trees with dense canopies were planted in front of housing schemes as sound barriers. The trees were planted in three different sizes; one, two and three to four metres tall.

Planting in median strip

This is another important aspect of planting in an expressway. The functional part of planting in the median strip is to provide a screen against glare at night caused by oncoming traffic.

The height of the plant screen depends on the degree of screening that is expected. On a flat road such as the CKE, a height of 1.4m is sufficient to cut off the light.

Here, an ornamental foliage shrub called Eugenia campanulata (Cristin) with pinkish green terminal young flush has been planted in two rows and turfed in between.

They should be pruned periodically to maintain a constant height of 1.4m. Along the Hunupitiya median strip, potted bougainvilleas were placed on the viaduct.

There are four interchanges along the CKE. They are at the New Kelani Bridge, Peliyagoda, Ja-ela and Katunayake.

The New Kelani Bridge interchange is planted with mixed ornamental shrubs incorporating natural rocks at random. Peliyagoda, the largest interchange, has been landscaped in an undulated manner by forming earth mounds with a slight gradient to look natural. This area is planted with ornamental shrubs, interspersed with medium trees. In addition, two rows of trees were planted along the boundary to form a green belt.

The Ja-ela interchange has been planted with mixed flowering and foliage shrubs on terraced lawns, each with a slight slope. The Katunayake interchange with an overpass towards the airport has been planted with multi-coloured bougainvillea plants.

These are potted in especially-made containers made of geo-textile embedded in plastic troughs that are fixed along the two edges of the overpass and along the viaduct. A drip irrigation system was provided for watering.

Two rows of Chrysalidocarpus lutescens (Cane palm) were planted on the lawn in line with the two edges of the overpass to cover the open space. A hedge of Acalypha siamensis has been established in front to prevent people crossing through.

Flowering shrubs

Both sides of the lawn are planted with flowering shrubs incorporating well-trimmed ornamental foliage plants such as Ficus benjamina, Eugenia campanulata, Cristin and a few drooping bougainvilleas. Shade-loving ornamental shrubs were planted around the old preserved Ficus benjamina tree.

The traffic island adjacent to the overpass is planted with dwarf flowering shrubs and turf. The height of these shrubs has to be maintained at about 60cm to prevent blocking the view of traffic from the airport direction to the main drive.

In all, around 70,000 plants including trees and shrubs have been planted along the CKE and are being maintained at the moment. Four landscape designers were assigned to carry out the landscaping and planting along the CKE and they completed the work on schedule, in an outstanding manner.

The landscaping and planting scheme was carried out with the guidance of Secretary, Ministry of Highways, Ranjith Premasiri, Project Director, Pushpa Gunaratne and Deputy Team Leader, Denzil Aponso. Officers of China Metallurgical Group Corporation and the Road Development Authority were prompt in action to solve the problems encountered during landscaping the highway.

The writer is Landscape and Horticultural Consultant to the CKE Project and Retired Superintendent of the Royal Botanic Gardens, Peradeniya.