NATIONAL PARK SERVICE
Park and Recreation Structures
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CROSSINGS AND CULVERTS

CLOSE COUPLING of these facilities is premised on a conception that the function of the culvert is to permit a trail or roadway to pass over a drainage obstacle, while the function of the crossing is to permit the drainage to pass over a trail or roadway. Paradoxically, their very difference thus closely relates them.

If in our approach to a park technique the primitive has the right of way, stepping stones for pedestrians and the ford have place as picturesque survivals. For horse trails and secondary motor roads in parks where traffic is leisurely and light, the ford is a legitimate and economical provision for crossing a shallow stream. This is subject to further reservations if tolerance of its quaintness is not to give way to annoyance on the part of the public. The low water crossing will not meet with favor if it is frequently impassable due to flood. Equally intolerable are a soft stream bed, treacherous holes, or other hazards to safe negotiation. The approaches must not incline too sharply, nor may sight lines, as the ford is approached, be obscured by planting. Lack of these requisites to public acceptance of the ford is apt to provoke clamor of disapproval and lead to demand for its replacement with a culvert or bridge, to the eventual voiding of the economy it was sought to effect.

In a sense the crossing is the bridge in embryo, the culvert, the boy that is father to the bridge. We are never unconscious of the presence of a bridge, however well it may be insinuated into environment. In its most minor expression it cannot possibly be truly inconspicuous. A culvert, on the contrary, being in reality merely a retaining wall pierced by a drain, can often be so treated that the casual passerby is unaware of its presence in a natural area. If culvert and fill are extended far enough to either side of the roadway, roadside planting may be extended across the culvert without interruption, and head walls may be omitted above grade. Planting will limit the width of traveled way with more naturalism and finesse than can possibly be achieved by obtrusive head walls. The latter close to the traveled roadway are at once alien and artificial and a traffic hazard.

If this procedure for subordinating culverts to surroundings is impractical or uneconomical by reason of terrain, head wall barriers then become a very necessary safeguard. Worthy of study is the character given the required barrier. Its artificiality can be held to a minimum. Like many another facility in natural parks, it should be first and always informal in treatment and blended to its surroundings. Materials and workmanship should be such that facing and culvert itself once constructed, make no demands whatever upon maintenance appropriations.

The culvert proper is sometimes of local stone when this is abundant and workable, but if it must be of concrete or of galvanized iron, reasonable concealment of the fact is to be striven for. The head wall, by extending well into the culvert opening, should avoid disclosing that it is a mere veneer. Natural rock is certainly the preferred material for the head wall, laid either dry or in mortar. The former method to be lasting must employ stones of suitably large size. If stone is not available, concrete or wood may be resorted to for the retaining wall. In a park sense, neither is a very satisfactory substitute for the stone wall.

Quite as much care should be given to the design and execution of culvert head walls as other park structures. Usual mistakes are insufficient care in the handling of mortar, resulting in sloppy joints, stone of trivial size, and lack of variety in sizes, leading to monotony and formality of surface pattern. These faults are common to much contemporary stone work, not limited to park construction only.



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Last Updated: 04-May-2012