Retention vs Detention Storage
When drought-weary observers of winter flood flows yearn for more storage capacity they are usually thinking of reservoirs retained by dams. But opportunities for detention storage are off most folks’ radar.
That needs to change, especially since the opportunities to expand/ restore detention storage are vast, in California and doubtless elsewhere. Humans have been unwittingly degrading watershed detention functions since our mastery of fire.
As defined in this site’s Glossary:
Retention: water is held against the force of gravity, above or within the soil. Within the soil, retention occurs within capillary pore spaces (micropores), where the retained water is available for uptake by plants. Above-ground retention is accomplished by dams or similar obstructions.
Detention: temporary storage of water. Below ground, soil water drainage by gravity is slowed, though not stopped, in macropores. Above ground, runoff is slowed by semipermeable means — most typically by routing through soil, but other means are possible.
Watersheds/ catchments restored with native cover types – uplands, along with expanded riparian zones and floodplains – will become increasingly self-sustaining, while their detention storage capacity increases over time. What’s not to love about that?