The safest way to build a retaining wall is to place it at the bottom of a gentle slope, if space permits, and fill in behind it. That way you won't disturb the stability of the soil. Otherwise, the hill can be held either with a single high wall or with a series of low walls forming graceful terraces. Hilly yards and retaining walls may call for a central catch basin. Always route water away from the house.
Steeper gradients are better for slow-draining, heavy soils.
Poor subsurface drainage can be a problem where the water table is close to the surface. Plastic drainpipes or dry wells can be the answer in many situations. But a major problem calls for a sump pump. To plan and install a drainage system for a problem hillside, get professional help. All rights reserved.