“Drowning in the Desert”

Revising the urban stream syndrome for the arid Southwest US

Stream hydrology controls stream health

Poff et al. (1997) “The natural flow regime” Bioscience 47: 769-784

Natural ground cover 10-20% impervious

35 to 50% impervious 75 to 100% impervious

Impacts of Impervious Surface

From National Research Council (2008) “Urban stormwater management in the US”

Natural ground cover 10-20% impervious

35 to 50% impervious 75 to 100% impervious

Impacts of Impervious Surface

From National Research Council (2008) “Urban stormwater management in the US”

Natural ground cover 10-20% impervious

35 to 50% impervious 75 to 100% impervious

Impacts of Impervious Surface

From National Research Council (2008) “Urban stormwater management in the US”

Natural ground cover 10-20% impervious

35 to 50% impervious 75 to 100% impervious

Impacts of Impervious Surface

From National Research Council (2008) “Urban stormwater management in the US”

Increased imperviousness leads to…

1: Too much water being delivered to streams during storms

2: Too little infiltration and not enough baseflow during dry weather

1+2: “URBAN STREAM SYNDROME”

Reversing the urban stream syndrome

Install distributed systems to capture/retain stormwater runoff and then…

• Reuse runoff in the home (e.g., toilet flushing)

• Infiltrate runoff to restore base flow• Return runoff to atmosphere through

evapotranspiration (e.g., green roofs, biofilters, constructed wetlands)

Reuse runoff in the home (e.g., toilet flushing)

• Conflicts with DHS guidelines (concern over cross-connections)

• Public health concerns• Practicality—in southern California runoff is

intense and short lived, toilet flushing goes on forever

Infiltrate runoff to restore baseflow

• Makes sense in many areas of the world• Makes sense in some areas of Southern

California– Deep groundwater recharge for drinking water

supply• BUT, baseflow in urban streams in southern

California has INCREASED, not decreased over the past 100 years*– Infiltration may not be appropriate in many areas

*Townsend-Small, Pataki, et al (2013) “Increasing summer river discharge in southern California, USA, linked to urbanization” Geophysical Research Letters 40:4643-4647.

Return runoff to atmosphere through evaporation/transpiration

• Green systems (green roofs, biofilters) are great but…– Concerns over long term maintenance– Plants with high ET are also unlikely to survive

during prolonged dry weather• Perhaps there is a role for “Wet systems” that

promote evaporation (e.g., fountains, cooling systems) when needed, but can be shut off when not needed

Vision for Prop 84 Proposal

• Grand Goal: Make UCI a Zero Discharge Campus by 2020

• Requires massive stormwater storage capability (up to 1500 acre feet per year)

• Requires new infrastructure for using the stormwater runoff

• Build a test facility on the UCI campus for innovative approaches to evaporate stormwater