Low-Tech Irrigation

Surface Irrigation Water flows across the soil surface to the point of infiltration Oldest irrigation method and most widely used world-wide (90%) and in U.S. (60%) Used primarily on agricultural or orchard crops

Types of Systems Water Spreading or Wild FloodingWater Spreading or Wild Flooding –Relatively flat fields -- allow water to find its own way across the surface –Minimal preparation and investment –Rather inefficient BasinBasin –Dikes used to surround an area and allow for water ponding (no runoff) –Basins are usually level (rice)

Basin Irrigation of Rice in SE Asia

Types of Systems, Contd… BorderBorder –Strips of land with dikes on the sides –Usually graded but with no cross slope –Downstream end may be diked FurrowFurrow –Small channels carry the water (entire surface is not wet) –Commonly used on row crops –Lateral as well as vertical infiltration –Furrows are usually graded

Water Supply Methods of water supplyMethods of water supply –Head ditch with siphon tubes or side-opening gates –Gated pipe (aluminum or plastic pipe with small gates that can be opened and closed)

Curve of Time Vs. Distance Distance from inlet end (ft)

Infiltration Profile

Flow In Ditches Manning’s Equation Q= Flow rate, cubic feet per second n= Channel roughness, n increases as roughness increases A= Channel cross-sectional area, square feet R= Channel hydraulic radius (Area / Wetted Perimeter), feet S= Channel slope, vertical feet/horizontal feet A WP

Uniformity Inherent non-uniformity because recession and advance curves are not parallelInherent non-uniformity because recession and advance curves are not parallel Factors affecting More Uniform Less UniformFactors affecting More Uniform Less Uniform –Inflow rate High Low –Slope Steeper Flatter –Soil infiltration rate Lower Higher –Roughness Smoother Rougher –Channel shape Higher R h Lower R h –Inflow time Shorter Longer –Length of run Shorter Longer

Irrigation Efficiency Volume balance basisVolume balance basis –E a = V z / V g = (V g - V r - V dp - V e ) / V g –Ea  Irrigation application efficiency (%/100) –V  Water volume g  gross (delivered to field)g  gross (delivered to field) z  net infiltration (stored in root zone)z  net infiltration (stored in root zone) dp  deep percolation (below root zone)dp  deep percolation (below root zone) r  runoff (beyond end of field)r  runoff (beyond end of field) e  evaporation (from furrow and wet soil)e  evaporation (from furrow and wet soil)

Microirrigation Drip, trickle, mist irrigation –Small flows (0.5-4 gallons/hour) per emitter –Low pressures (6-15 psi) Good for row crops –Line source emitters Good for orchards & vineyards –Point source emitters

Drip Irrigation Design Considerations Determine the number of emitter lines/bed and emitter spacing based on soil type and bed width. Sand-low capillarity Loam-medium capillarity Clay-high capillarity Use 2 dripper lines on wide beds with sandy soil

Drip Emitter Line Characteristics Drip tape Used primarily in row cropsUsed primarily in row crops Emitters formed into seam during manufactureEmitters formed into seam during manufacture Operating pressure: 6-15 psiOperating pressure: 6-15 psi Flow rate: gpm/100 ft (0.5 most common)Flow rate: gpm/100 ft (0.5 most common) Emitter spacing: 8-18 inches (12 most common)Emitter spacing: 8-18 inches (12 most common) Wall thickness: 4-25 mil (8-mil most common)Wall thickness: 4-25 mil (8-mil most common) Length of run: ft (5/8-inch tape)Length of run: ft (5/8-inch tape) Drip tape Used primarily in row cropsUsed primarily in row crops Emitters formed into seam during manufactureEmitters formed into seam during manufacture Operating pressure: 6-15 psiOperating pressure: 6-15 psi Flow rate: gpm/100 ft (0.5 most common)Flow rate: gpm/100 ft (0.5 most common) Emitter spacing: 8-18 inches (12 most common)Emitter spacing: 8-18 inches (12 most common) Wall thickness: 4-25 mil (8-mil most common)Wall thickness: 4-25 mil (8-mil most common) Length of run: ft (5/8-inch tape)Length of run: ft (5/8-inch tape)

Drip Emitter Line Characteristics Hard Hose Used primarily in perennial cropsUsed primarily in perennial crops Emitters glued into hose during manufactureEmitters glued into hose during manufacture Operating pressure: psiOperating pressure: psi Flow rate: gph/emitterFlow rate: gph/emitter Emitter spacing: inchesEmitter spacing: inches Length of run: varies depending on hose diameter, emitter spacing and emitter flow rateLength of run: varies depending on hose diameter, emitter spacing and emitter flow rate Hard Hose Used primarily in perennial cropsUsed primarily in perennial crops Emitters glued into hose during manufactureEmitters glued into hose during manufacture Operating pressure: psiOperating pressure: psi Flow rate: gph/emitterFlow rate: gph/emitter Emitter spacing: inchesEmitter spacing: inches Length of run: varies depending on hose diameter, emitter spacing and emitter flow rateLength of run: varies depending on hose diameter, emitter spacing and emitter flow rate Pressure compensating In-Line On-Line

Drip Emitter Line Characteristics Hard Hose Used primarily in perennial cropsUsed primarily in perennial crops Emitters installed in holes punched in hoseEmitters installed in holes punched in hose Custom emitter spacing: inchesCustom emitter spacing: inches Operating pressure: psiOperating pressure: psi Flow rate: gph/emitterFlow rate: gph/emitter Length of run: varies depending on hose diameter, emitter spacing and emitter flow rateLength of run: varies depending on hose diameter, emitter spacing and emitter flow rate Hard Hose Used primarily in perennial cropsUsed primarily in perennial crops Emitters installed in holes punched in hoseEmitters installed in holes punched in hose Custom emitter spacing: inchesCustom emitter spacing: inches Operating pressure: psiOperating pressure: psi Flow rate: gph/emitterFlow rate: gph/emitter Length of run: varies depending on hose diameter, emitter spacing and emitter flow rateLength of run: varies depending on hose diameter, emitter spacing and emitter flow rate Simple On-Line Pressure Compensating On-Line

Low-Tech Irrigation Pumps Gravity assist bucket pump (2.31 ft of elevation = 1psi) Human-powered step pump 4.6 ft = 2 psi

Homemade Drip Line Orifice Discharge (gph) Nominal Operating Head Hole Diameter 3 ft 4 ft 5 ft 6 ft 7 ft 8 ft 1/16 in /32 in /8 in

Microirrigation Uniformity Low emitter flow rates (0.5 – 1 gph)Low emitter flow rates (0.5 – 1 gph) Wide emitter spacing (2 - 4 ft)Wide emitter spacing (2 - 4 ft) Large lateral line diameter (> ½-inch ID)Large lateral line diameter (> ½-inch ID) Short lateral length (<300 ft)Short lateral length (<300 ft) Slight lateral downslope (1/2 – 1 %)Slight lateral downslope (1/2 – 1 %) High lateral inlet pressure (10+ psi)High lateral inlet pressure (10+ psi)

Microirrigation Filtration Home Made Sand Filter - Perforated pipe collection gallery - Graduated gravel bed - Washed sand filter media

Resources Mike Kizer’s Homepage – OSU Extension Facts – ument-1443/BAE-1511web.pdf