Swale Question

Santoyo & Associates santoyo at earthflow.com
Sun Jun 3 17:00:26 EDT 2001


Claude, (Vint, Toby, et al),

Vint and Toby have had excellent points for you.  Remember too that 
swales and water catchments are only one half of a calculated 
response to (specific) landscape dynamics.  Plants (trees, perennials 
and annuals) make up the other half of the equation -"converting 
infiltration to biomass" is the sound bite.

The usual argument against water catchment is about depriving surface 
streams of overland flow.  The response to that argument is that; 
although swales and other catchments do reduce overland flow -the 
best and most significant thing that infiltration does is to increase 
"baseflow" of surface waters through groundwater recharge (as opposed 
to surface runoff) -baseflow is much better quality of water and 
contributes over a significantly longer duration.

As with all techniques and technologies it is in fact only 
appropriate if it is truly filling a need (solving an issue ie; 
aforestation and reforestation, reduce flooding problems, etc...) 
You wouldn't want to infiltrate more than the soil could safely hold. 

Maybe a better question is when would you not want to use water catchments...
I'll tell you some mistakes I have made and have seen -You don't want 
to work on too steep or too shallow of a soil profile, even in the 
northeast but especially in the west, bedrock can be quite close to 
the surface especially on hills...under those conditions, cutting 
swales for infiltration has caused landslides, flooding and erosion - 
it can all be mitigated through calculating coefficients of run-off 
friction and saturation rates to determine the frequency and depth of 
catchments -to be safer, novices should stick to working on less than 
15 degree slopes.

One idea that I came up with (after I caused a small landslide) is, 
instead of making the water soak down quickly into the soil, make it 
soak up! ..as in wick up into a row of compost or straw bales on 
contour end to end, allowing a slower release.  This technique has 
proved successful in both a "woods-cultivated" ginseng crop that I 
installed in upstate New York and a hillside olive grove in coastal 
California.

In addition to WATER FOR EVERY FARM, check out PRINCIPLES AND 
PRACTICES OF GRADING, DRAINAGE AND ROAD ALIGNMENT: AN ECOLOGIC 
APPROACH by Richard K. Untermann (available from  the bookstore at 
<http:www.permaearth.org> )


Larry Santoyo
San Luis Obispo, California
1.800.469.5857
santoyo at earthflow.com
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