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Surface depression

A surface depression is a depressed area in a reinstatement having generally smooth edges and gently sloping sides; see Figure S2.3. Intervention is required where the surface depression spanning more than 100 mm in any plan dimension exceeds the intervention limit X shown in Table S2.1.
Figure S2.3 Surface depression intervention limit
Earlier intervention is required if the depression alone results in standing water wider than 500 mm or exceeding 1 m2 in area, at 2 hours after the cessation of rainfall.
Table S2.1 Intervention limits for surface depression

Reinstatement width W (mm)

Intervention limit X (mm)

Combined defect intervention limit (mm)

Up to 400 10 10
Over 400 to 500 12 10
Over 500 to 600 14 12
Over 600 to 700 17 14
Over 700 to 800 19 16
Over 800 to 900 22 18
Over 900 25 20