Chapter 5: Quantifying Benefits

5.1 Estimating Benefits

Can we afford clean water? Can we afford rivers and lakes and streams and oceans which continue to make possible life on this planet? Can we afford life itself? Those questions were never asked as we destroyed the waters of our nation, and they deserve no answers as we finally move to restore and renew them. These questions answer themselves.

—Senator Ed Muskie

Based on analysis of information provided by the stakeholders, if all the projects presented in Chapter 4 were implemented (the preferred project scenario), we could potentially increase our local water resources by 38,865 acre-feet a year. That’s enough to provide nearly 80,000 families of four with enough drinking water for an entire year.

This would indicate that by making some simple modifications in our land use and development practices, we could have more water supply, better water quality, improved public safety, more open space, and increased habitat. How do we know this? In general terms, experience with recent projects can be extrapolated to other proposed projects of a similar type.

The County’s Tujunga Wash Greenway Project now accepts diverted flows the Pacoima Wash Channel and infiltrates them to groundwater through a re-created linear stream adjacent to the channelized Wash (project no. 9 in Chapter 4 would extend the greenway northward). Based on initial monitoring, the County calculated that the project will infiltrate 325,000 gallons of water a day—enough water for 760 families of four for a year. As those flows are eliminated from the main channel flows, flood safety is also enhanced. Additionally, the project provides some native habitat and creates new pedestrian and bicycle linkages for the community.

The retrofit of Big Tujunga Dam (project #26 in Chapter 4) now underway are estimated to provide 5,000 acre-feet/year of additional storage capacity, enhancing flood safety. Some of these additional volumes can now be more effectively diverted to spreading grounds for infiltration. In addition, these more thoughtful flow releases can benefit aquatic species habitat.

NorthEast Trees recently partnered with the City of Los Angeles to create a “green street” on Oros Street in the Elysian Valley area, adjacent to the Los Angeles River just upstream of the confluence with the Arroyo Seco. The project captures stormwater runoff from private homes and a residential street and cleans it through a series of soil filtration and vegetative treatments before discharge to storm drains and the Los Angeles River. The project also improves and beautifies a neighborhood with new green infrastructure that addresses both storm and dry weather runoff.

The Los Angeles and San Gabriel Rivers Watershed Council (LASGRWC) is partnering with TreePeople and the City of Los Angeles to undertake a neighborhood retrofit on Elmer Avenue as a demonstration project of the Water Augmentation Study (WAS), in the Sun Valley watershed, immediately adjacent to the Tujunga/Pacoima. The project aims to capture stormwater and dry weather runoff from approximately 40 acres of residential land use to reduce significant flooding, improve water quality, increase groundwater recharge, and beautify the neighborhood with native habitat. The project is designed to handle greater than a 2-year storm or approximately 80 percent of the annual rainfall and is estimated to infiltrate greater than 13 acre-feet of water annually. This $1.5- to $2-million project is funded by California State Department of Water Resources, U.S. Bureau of Reclamation, and the WAS partner agencies.

The latest data from the 8-year-long LASGRWC Los Angeles Basin WAS shows that stormwater infiltrated to groundwater in the east San Fernando Valley causes no measurably negative impacts to groundwater quality for a wide range of contaminants. This indicates that storm water projects can be less heavily reliant on expensive technological solutions to meet water quality improvements, making them more cost effective overall. And every time we undertake a project, we learn more about what works. Further, the more projects we do, the greater the economies of scale.

LADWP is now using some rough estimates to calculate the potential water supply, flood reduction, and economic benefits of proposed projects. While the precise benefits are always project and site specific (i.e. soil conditions, extent of project, size of drainage area captured, etc.), the following general estimates can be utilized: In dry weather, soils are well drained and thus most receptive to infiltrating stormwater, so it is possible to get a lot of water (approximately 1 ft/hr) into the ground instantaneously. After complete saturation of the soil occurs (steady state), it is possible to infiltrate approximately 1 cubic foot per second (cfs) per acre of infiltration area. In a simulated wash or maintained recharge basin, that can equal 2 acre-ft/day. Every cfs infiltrated into the ground frees up downstream flood conveyance capacity by an equal amount.

While these amounts might not seem great, the water supply benefits can be estimated at about $300 per acre-foot of recharged water, and LADWP pays approximately $6,000 per cfs for peak conveyance costs. Assuming a project life of +/-30 years, the overall water supply benefit per acre-foot recharged equals $9,000. And if flood control is considered an annual benefit, the overall flood protection benefit over the life of a project may potentially exceed $180,000.

Based on the projects and conceptual estimates noted above, we can see that there would be clear benefits to undertaking a watershed approach for water supply, water quality, and public safety. Habitat benefits are harder to quantify, but implementation of the plan scenario would result in an overall increase in open space and associated native vegetation, and increased access to parks. In addition, it would be more cost effective overall than our current approach.