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Poor drainage is the cause of most problems in path management. A typical situation on a path enclosed by hedges or walls is that surface and sub-surface water collects and causes waterlogging and puddles of standing water. Trampling compacts the wet ground, further impeding drainage. Waterlogging prevents the growth of grasses and other vegetation which would help protect the surface. The path becomes a morass of mud in wet weather, and even in dry conditions has a pitted, uncomfortable surface on which to walk.
On unenclosed paths walkers simply avoid the muddy patch or puddle, so spreading the trampling and destruction of vegetation and soil structure, until a wide area may be affected. On enclosed paths walkers may make new paths along hedge banks to avoid the mud, or trespass on adjoining land.
On slopes the damage is not just to vegetation and soil structure, but to the ground itself, which is washed away as water runs down the slope. A typical cycle of events is that vegetation on slopes is worn away by trampling, which exposes the thin soil to rapid erosion by water running down the path. This leaves a loose and slippery path, which is abandoned in favour of another line, that is then rapidly reduced to the same condition.
Once a path is formed and the vegetation lost, the path itself becomes a factor in slope drainage. The path interrupts, and may divert surface flow or groundwater seepage. The path may become a significant drainage line, with resulting erosion. Trampling on the path compacts the soil and accelerates water flow, and the bare ground is exposed to rainsplash, frost-heave and mass movement of saturated substrate.
The catchment area has a great influence on the amount a path will erode. Hilltop ridge paths, though developing quickly due to concentrated use and thin soils, usually then remain fairly stable due to the limited catchment of water.
The techniques described in this chapter are for draining water off and away from paths. The techniques for building stone cut-offs and drains are also used for much larger- scale slope drainage, where erosion has occurred over a wide area, and vegetation restoration is needed. This is discussed further in Chapter 11 – Erosion control and vegetation restoration.