Problem-Solving – Bridging Water

“I have a naturally very wet area in the garden that floods at certain times of the year. I intend planting it as a bog garden, but I need some means of access to get the most enjoyment from the feature and for essential maintenance. Is there any way of creating a suitable duckhoard or boardwalk arrangement?”

Duckboards are an excellent way of bridging broad stretches of still water or boggy areas. They should be supported on wooden cross-members attached to posts set in the ground.

The supporting posts should be driven into the ground to a depth of at least 45cm (18in), and at intervals of about 2m (6ft) across the site. Ideally, the timber should be tanalized to ensure a long life. They can be rounded or square, and the crossmembers can be attached to them by means of cross halving joints and bolts, or simply bolted flat against them. Crossmembers should be set below the tops of the posts so that the latter extend slightly above the boards.

The boards themselves should be sturdy and similar in size to scaffold boards. As with the supports, they are best tanalized, and they should be secured with rustproof screws.

Although duckboards will produce a very straight and formal feature, variation and interest can be created by setting the boards at right angles to one another at intervals across the bog garden. The boards need not all be of the same length either. However, they should always be installed level, for sloping duckboards can be dangerous, even if covered with fine-mesh wire netting to improve grip on the slippery wood.

Normally, a handrail will spoil the effect of a duckboard walk and, for the most part, will he unnecessary. However, when such a feature runs out into an open body of water, terminating in a viewing area, a simple rail is worth adding for safety’.s sake.

An alternative to conventional duckboards is the rustic log walkway, which also fits in well with a bog garden area. It requires similar supports to the duckboard walk, but instead of running lengthways, the logs are placed across two strong supporting rails. These should be tanalized and bolted to the posts, the log sections being bolted to the rails. Rounded logs will be difficult to fix, even if quite small, so they must be sawn through lengthways to produce a flat surface to rest on the supporting rails. The log sections should be pushed together to create an almost corrugated effect.

Tanalizing is also important for the logs, which as far as possible should retain their bark. Pine is the best timber for this purpose, since the bark is not only attractive, but also it usually remains on the timber, despite the passage of feet. Normally, wire netting is not necessary on such a walkway, as the bark provides grip. However, it must be inspected regularly, for despite the best preservative treatment, logs will not last as long as more conventional planed planking.

 

“I have seen a natural turf bridge, which I think would be ideal for my garden, providing a continuous link from one lawn to another across a stream. How do I set about creating such a feature?”

Almost any form of construction can be used to provide support for a turf bridge, including brick and stone. However, sufficient depth of soil and good drainage are both essential if the grass is to succeed. For this reason, slab and concrete supports are undesirable, since the turf will either dry out or become very wet and soggy.

Although unconventional, the best supports for such a bridge are substantial logs, such as poplar or elm. These will last for many years before they need replacing. Ideally, the logs should be 30cm (12in) or more in diameter. Lay them across the stream, pushing them together and sinking their ends into the banks, but make sure that there is sufficient clearance beneath the logs to allow the passage of winter water. Push the logs together and create a small upstand along each side of the bridge, using smaller diameter lengths of the same timber. If desired, hand rails can be fixed to the sides at the same time.

The upstands retain a layer of soil and the turf, and should be large enough to ensure that the depth of soil and turf combined is at least 10cm (4in). Spread a layer of polythene, pierced with drainage holes, over the logs first to prevent the soil from falling through the gaps between them. The turf is laid on the soil in conventional fashion and should be kept well watered for the first season. It will establish quickly, and once it has knitted to the lawn on each side, a certain amount of natural moisture transfer will take place, and unless you experience unseasonably hot weather, it should remain green.

If the grass turns brown and struggles in the summer, top-dress with peat in the spring, aerating the turf to break up compaction and admit air. Dust sharp sand into the holes, adding some of the moisture-retentive gel crystals used for hanging baskets. This ensures the retention of moisture in the turf and a continuous green sward all summer long. Do not neglect to feed the turf either; a liquid lawn fertiliser applied twice during the summer will be beneficial.

 

“I would love to have a small arched stone bridge, but 1 cannot find anyone who can make one. Is there any alternative for a similar effect?”

It is very difficult to find a stone worker who can construct an arched garden bridge. A similar effect can be achieved using concrete and suitably cut stones.

The base of the bridge can be constructed of concrete with metal reinforcing, using well supported marine plywood shuttering to create a suitable curve. Providing that the stones that you use are cut to look as if they curve, they can be bedded into the concrete. For extra security drill each stone, insert a short length of metal rod and set this into the concrete. Once the first layer of stones is in position, a parapet can be constructed and the second stone layer can be tied into the concrete base of the bridge, which will further secure the curved bottom layer. Once the concrete has set firmly, the plywood shuttering can be removed.