SA Cistern Notes

• Rainfall data from TCEQ: http://www.tceq.state.tx.us/cgi-bin/compliance/monops/monthly_summary accessed 2007-05-07
• (100×30)m2 0.3 ha total: (60×30)m2 0.2 ha orchard, (30×30)m2 0.1 ha garden vegetables (cultivated area)
• NCSU has a nice report on vegetable crop water needs.
  • “application rates should not exceed[…]0.20 inch per hour for clay soils”
  • Vegetable crops require 2.5 cm/21days 2.5cm/5days
  • = 0.05-0.2 in/day = 0.125 to 0.5 cm/day ; 1.5 to 5 m3/day = 500 to 2000 m3/yr for 0.1 ha of crop area with year-round cultivation. ¹⁾

A more realistic estimate of land use is needed; not all the area is under cultivation at all times. Some area is used for walkways, and at any given time, some is fallow or planted with drought-tolerant (sometimes non-food) crops. Also, some of this is orchard.

• (60×30)m2 orchard planted (2×4)m is (15*15)=225 trees; 225*(0.025|0.040)m3/day = 5.6 to 9 m3/day during the growing season; less during winter.
• (60×30)m2 orchard planted (4*5)m is (15*6)=90 trees; 90*0.11356²⁾ = 10 m3/day
• 2000 m2 * 0.75 shaded * 10.764 ft2/m2 * 0.125 gal/day-shadedft2* 0.0037854 m3/gal = 7.6 m3/day

Here is some info for fruit tree irrigation.

• Plants over 4 feet in diameter: gal/day = 0.125 X shaded area
• Plants less than 4 feet in diameter: gal/day = 0.17 X shaded area

It looks like a total of about 10 m3/day is needed, on average, for the 0.3 ha area of orchard and garden. To go a full season (worst case for the garden) would take about 1000 m3 storage, a tank 25×10*4 m.

Approximate water requirements for mature trees and plants:

Examples of daily water use.