Altadena Drainage Plan & Hydrology Report on Marathon Road

Because we kept all slope transitions at or under 5:1 (20%), the project qualified as a drainage plan rather than a full grading plan, which simplified LA County approval. Grading plans are required when moving over 500 cubic yards of earth, working in hillside areas, or excavating for basements and pools.

Only if post-development stormwater flow exceeds pre-fire conditions. On this Marathon Road lot we routed area and trench drains by gravity into two lined rain gardens at the rear, so the hydrology report showed flow would not exceed pre-fire conditions and no sump pump was needed.

A steeper lot requires more careful grading to work with the natural slope. This 0.1309-acre lot drops about 10 feet from street to rear over 114 feet, which we worked with by using shallow 5:1 transitions, an 11-step rear deck, and drain capacity sized accordingly. Hillside lots over 20% can also trigger shoring and geotechnical coordination.

For single-family residential Altadena fire rebuilds we use standard pricing: drainage plans are $4,400 and hydrology reports are $2,400 when drainage must cross the property. Most Altadena lots require both due to the hillside terrain and county requirements.