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Stormwater Case Study | The Oak Grove Altadena

A Fresh Stormwater Solution & New Development in a Historic California Community


Altadena is a historic turn-of-the-century Los Angeles enclave nestled along the hills of the San Gabriel Mountains. The town’s personality is founded in it’s natural surroundings, from countless parks and recreational areas, national forests, to contributory waterways. And although Altadena’s roots are tied in agricultural development, food production, and dairy processing, the town is now recognized for a legacy of water preservation, agricultural controls/balances, and iconic craftsman architecture. Protecting it’s natural surroundings, environment and resources are all shared priorities of the community and custodians of the local Arroyo Seco Watershed.

According to the Arroyo Seco Watershed Organization, “The watershed is a subwatershed of the Los Angeles River Watershed, a basin between the San Gabriel Valley and the San Fernando Valley.”1 The Arroyo Seco watershed is one of California’s most important watersheds, and it has been designated as an impaired waterway for sedimentation/erosion and aquatic habitat degradation due to urbanization.

couple sitting on a bench at altadena park

Water quality goals for the watershed and surrounding areas include restoring hydrological function, flood control, conserving water resources, and improving water quality to enhance natural open areas and recreation. And the community’s methods for addressing stormwater greatly affect each water quality goal and impact their progress for the surrounding environment and wildlife.

Stormwater Goals & Challenges

The Oak Grove of Altadena is a new housing development project facing some obvious challenges, from saving land, architectural aesthetics to water quality, and infrastructure. But the development will deliver value to the community like new housing options and infrastructure improvements along with improving site-controlled water quality and drainage.

The project will include a stormwater management system with natural drainage beds and precast engineered underground storage tanks to collect and filter stormwater runoff from the site. The system is intended to protect the environment by capturing and filtering potential water pollution caused by rainwater before it enters local groundwater aquifers, streams, or other bodies of water; as well as real estate. Oak Grove’s design will also mitigate and control high volumes of stormwater runoff which contributes to flooding in low-lying areas, including parts of Altadena, offering the community a return on a preferred infrastructure investment.

Stormwater Design

The Oak Grove lot is a very compact space with variable elevations and slopes. This can make drainage details and piping complicated while designing/planning to capture and infiltrate required stormwater volumes. Downstream of all site runoff is a set of cisterns and settling chambers that effectively conserve land and development space.

Diagram 1: Stormwater Drainage Plan

All stormwater collected from roof gutters will have downspouts that connect to underground storm drains which feed surrounding bioretention treatment basins. Stormwater from bioretention treatment basins will ultimately be discharged into primary stormwater collection systems located underground and within designated ‘green’ areas of the development.

See Diagram 1: The Drywell configuration and the basic elements of the stormwater drainage plan.

Stormwater Solution

What are Drywell stormwater systems?

Well-designed drywells can manage a large amount of water volume, and Santa Fe Water Systems’ Drywell design administers a fresh multi-faceted solution to meet complex stormwater goals and manage runoff. Drywells are cost-effective solutions that can handle high volumes of water in a small footprint and can be custom-built to fit a site’s needs. They also allow for the capture of water that would otherwise sheet flow off a property or overwhelm stormwater systems or local watersheds.

According to the California Water Resources Control Board, “Dry wells not only aid in stormwater runoff reduction, but they can also increase groundwater recharge, are economical, and have minimal space requirements.”2

Santa Fe Water Systems provides designs and production of the stormwater industry’s Drywell system, offering engineers and developers an efficient and immediate solution for a wide range of stormwater goals. Contact us today for a project review session or preliminary design [Link].


The Oak Grove of Altadena development is a considerate response to California’s rising housing demand and the need for more affordable housing in Altadena and Los Angeles County. The project created 15 new single-family homes, open space, and protections for valuable existing vegetation and historical trees. It also addressed stormwater management by creating a crucial set of drywells (infiltration basins) that absorbed water from rainstorms and reduced flooding risks from future storm events.