Earthworks
CTED, Ithaca 2015
Steve Gabriel
What it’s all about:
- learning to read the landform (contour!)
- designing to catch & store water for the longest time, over the longest distance possible
- creating biological landscapes that are resilient to flood + drought
Best Strategies for Water Catch & Store:
1) Rainwater Catchment (small scale – up to 1,000 gal)
2) Earthworks (small to large scale)
3) Trees, plants, mulch (biology)
1. Rainwater Catchment
For potable water: add pellet chlorinator or UV before storage tank.
Use 55 gal drums, 275 gallon cube tanks, 1,000 gallon septic tanks
Roof water calculations:
Harvested Water (gal) = catchment area (ft2) X rainfall (in) X .632
Need to calculate for annual (36”), monthly (3 – 4”), and pulse (1”, 2”, 4”)
(http://rainwaterharvesting.tamu.edu/catchment-area/)
First flush calculations:
Installing a first flush dramatically
improves water quality
General estimate: First flush should
remove about a minimum of 10
gallons per 1,000 sq feet (more in
polluted environments)
http://www.harvesth2o.com/first_flush.sht
ml#.VQbzwGZ8Ljo
TEST your water regularly if you plan
on drinking it!
Earthworks (the “sand pile”) - Brad Lancaster – www.harvestingrainwater.com
- Shaping the landform to infiltrate or infiltrate and drain water in the landscape
- Investment of labor/fossil fuels to leverage storage, edge, function for long term
- Integrated systems of earth elements that move, infiltrate, and store water in the landscape
- One of the first things you do, and THE thing you do correctly and pay good money for
Earthworks are necessary and ethical where they:
Reduce our need for energy (berm for a house, gravity fed water, reduced water needs)
Diversify our landscape for food production (aquaculture)
Permanently rehabilitate damage (contour banks, check dams)
Enable better land use or help revegetate the earth.
See “Greening the Desert” https://www.youtube.com/watch?v=xz
THjlueqFI
A. Contour – defining patterns in
the landform
How do you find it on paper, landscape?
Paper:
USGS survey (20 foot contours)
Google Earth trace
Hire a surveyor!
Land:
A-frame, Water Level, Laser Level
B. Ridges, valleys, watersheds – always nesting
C. The four parts of the temperate landscape
D. Impacts of slope, elevation, aspect
E. Consider placement of ponds, swales, terraces, gabions, septic, greywater
* START AT THE HIGH POINT(S) OF THE LANDSCAPE
* ALWAYS PLAN FOR OVERFLOW AND MANAGE AS A RESOURCE
* ALWAYS SEED & PLANT IMMEDIATELY AFTER EARTHWORKS
Ponds: dam wall, key, spillway (a swale) are
critical
Need at least 60% clay to build a natural pond
Is there enough catchment to keep pond full?
(see below)
Swales: level, or slightly off contour (1”:300’ to 1”:25’)
Goal is to harvest water runoff, infiltrate within 24 – 28
hours
Terraces:
Mark
contours
as
pathways,
dig out,
level beds
in between
Septic & Greywater:
Existing septic: use for grazing, squash, pumpkins, etc (nothing deep rooted)
See: https://pubs.ext.vt.edu/426/426-617/426-617_pdf.pdf
Greywater: can be moved into mulch pits and basins
See: Creating an Oasis With Greywater, Art Ludwig
F. Calculate catchment areas + capacity
To calculate runoff you need to know the square footage (catchment area) of your site, your annual rainfall
estimate, and your estimate runoff coefficient (some provided below).
Runoff coefficient relates the amount of runoff to the amount of precipitation received. It is a larger value for areas
with low infiltration and high runoff (pavement, steep gradient), and lower for permeable, well-vegetated areas
(forest, flat land).
Then use this formula:
catchment area (ft2) X rainfall (convert to ft) X 7.48 gal/ft3 X runoff coefficient = net runoff (gal)
For example - a six-acre site:
261,360 ft2 X 3 ft X 7.48 gal/ft3 X .2 = 1,172,984 gallons of water per year.
Note: 1 acre = 43,560 sq ft
Again, try looking at ANNUAL (3’), MONTHLY(.25’), and PULSE RAIN EVENTS (.10’ - .25’) to get a sense of the patterns.
Some runoff coefficients:
City
Urban areas
0.70 - 0.95
Lawn/Field
Sandy soil, flat, 2%
Sandy soil, avg., 2-7%
Sandy soil, steep, 7%
Heavy soil, flat, 2%
Heavy soil, avg., 2-7%
Heavy soil, steep, 7%
Agricultural land
Bare packed soil
Cultivated rows
Pasture
Woodlands
0.05 - .10
.10 - .15
.13 - .17
.15 - .20
.18 - .22
.25 - .35
0.30 - 0.60
0.20 - 0.50
0.15 - 0.45
0.05 - 0.25