california; managing rainwater - sierra watershed, coastal san luis resource conservation district

Managing Rainwater

Regina Hirsch

Sierra Watershed ProgressiveSierra Watershed Progressive

Why?Why?

Why Manage Rainfall?Why Manage Rainfall? Slow erosion

Reduce mud areas

Water livestock

Irrigate pasture

Provide supplemental water supply

Decrease nuisance pests from unwanted pooling or flooding

When water speeds up

Why manage rainfall?•Enough rain falls in the United States each year to cover our country to a depth of 30 inches.

•How much falls in your watershed? On your ranch? In your yard?

•San Luis Obispo receives 27 billion gallons per year, on average

•27,154 gallons per acre per one inch rain storm

How fast does water move?How fast does water move?

Residence Time (USGS)

Antartica 20,000 years

Oceans 3,200 years

Glaciers 100 years

Groundwater Shallow: 200 years

Groundwater Deep: 10,000 years

k Lakes 100 years

Rivers 2 to 6 years

Why manage rainfall?Thirty percent of all runoff has turned to flooding or erosion problems due directly to our changes in the watershed infiltration dynamicchanges in the watershed infiltration dynamic.

How?How?

How best to manage runoff?How best to manage runoff?

Catch it first! Slow it move it store itCatch it first! Slow it, move it, store it

Rainwater tank catchmentRainwater tank catchmentTank catchment requirements:

•Cover•Cover

•Coarse debris filter

•Overflow

•Drain

•Manhole access

•Sanitary extraction

•First flush (where/when appropriate)

•Backflow or check valve

Rainwater Tank StorageRainwater Tank StorageAdvantages Disadvantagesg Disadvantages

Cleanest supply of water Readily available where needed

Tank storage can be cost prohibitive

Soft water Owner-operated and managed Promotes self-sufficiency

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Stored water is heavy, local codes may vary on

i i /f d ti dPromotes self sufficiency Conserves other water resources Low running costs

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seismic/foundation needs

Leakage on steep slopes can cause undercutting of footing

Flexible technologies Safe for human potable use if treated Reduces erosion, flooding, and other

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Can be unsafe for small children if installed i lstormwater runoff effects improperly

How Big a Tank?gHow much water do you need in rainfall months? In dry months? Total? Annual Water Need?

Gallons/week350

How much rainfall do you receive in a drought year?

Annual Rainfall?Inches/year

18

Rainfall intensity? 1 05How much rainfall do you receive in an hour?

How many months does it go without raining?

Rainfall intensity?Inches/hour

1.05

Dry weeks? 14ow a y o t s oes t go w t out a g?

How big is the surface you are catching off of?Size of harvesting surface? Sq/ft

1000

What is the roof and gutters made out of? Surface permeability? 90%

SURFACE POTENTIAL: Surface area (800) x .623 x Annual rainfall (18) x Perm. (90%) = 10,092 gallons

STORAGE NEED: Need (350) x Dry weeks (14) =4900 gallons

T k C id tiTank Considerations•Not opaque

•Lighter color keeps water cooler

•Potable plastic if for quality drinking water

•Non-galvanized if used for irrigation (or use liner)

•Underground tanks should have swivel unions and flexible lineswivel unions and flexible line

•Covered, but accessible

•Seismic requirements for larger tanks especially verticaltanks, especially vertical

Other Other tank options

T k D d D ’Tank Dos and Don’ts

Do: Don’t: Use a vertical tank on the highest point possible. This gives

options to distribute via internal tank pressure.

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Never use sand as a base for tanks. Shifting and erosion can undermind footing and Low pressure valves can work off as little as 7 psi. Use

0.433 psi gain per foot of elevation from water holding surface.

Bring water in ‘quietly’ to let fines settle and stay below

can undermind footing and cause tanks to shift and move.

Never leave a tank empty in a freezing climate.

Bring water in quietly to let fines settle and stay below extraction zone.

Always leave room for expansion of joints and use appropriate bulkhead materials.pp p

For best water quality, use a floating extraction hose set for the upper ¾ of the tank, but not from the top.

For long term storage, leave 1/6 of your tank unfilled to g g , ykeep water aerated.

Post all plumbing with “rainwater, non-potable”

First Flush, Filters, and Siphonspto have or not to have?

Topographical Rainwater Catchment•Best suited for decreasing Best suited for decreasing stormwater runoff

•Increasing groundwater and interflow water quantitiesq

•Best done on slopes less than 5%

•Basins are filled with mulch and planted to filter and slow water

SLOW it DOWN, SOAK it UPBerms and swales on contour slow surface runoff. Planting these basins will aid in soaking up extra water inflitration.

Basins are planted with appropriate trees that can provide needed shade cover for livestock and soilBasins are planted with appropriate trees that can provide needed shade cover for livestock and soil.

SLOW it DOWN, SOAK it UP

SLOW it DOWN, SOAK it UP

Tools and ResourcesTools and Resources

ToolsLevel (water level)

A frame or survey stadia rod and scope

Measuring tape

ResourcesResourcesCost Effective Tank Shoppingpp g

Local Community Services Districts

Watershed Groupsp Ebay General Contractors Car Washes

Water Information Resources

Car Washes

ARCSA www.arcsa.orgARCSA www.arcsa.org SLO Green Build SLORCD

d Texas A&M Rainwater Guide Harvesting Rainwater, Brad Lancaster

Site DesignSite DesignCHECKLIST

•Solar and wind aspect

•Existing tree and shrub community

•Rough topography map

•Neighboring waterways

S il i i•Soil composition

•Percolation rate

•Drainage plot

R i t k h t•Rainwater worksheet

•User needs and accessibility

•Other resource inventory

“As soon as you start doing, you learn how to proceed.”B Mollison-B. Mollison