Irrigation Water Supply

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Irrigation Water Supply
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The Hydrologic Cycle
3
Surface Water

• Streams and rivers
• diversion by gravity flow or pumping
• often low flows when irrigation water is needed
  most
• Lakes, ponds, reservoirs
• gravity flow or pumping
• source of water need for replenishing

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Average Annual Precipitation in Oklahoma
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Annual Evaporation from Free Water Surfaces
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Average Annual Runoff from Watersheds (acre-inches
of runoff/acre of watershed)
USGS, 1975
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Hydrologic Considerations

• Panhandle Calculation (Guymon, OK)
• Rainfall 18 in/year
• Evaporation 63 in/year
• Runoff 0.3 acre-inch/acre
• Loss 63-18 45 acre-in per acre of lake
• Gain 0.3 acre-in per acre of watershed
• Need 45/0.3 150 acres of watershed per acre
  of lake (just to offset evaporation loss)

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Wastewater Sources

• Agricultural and municipal wastewater are
  frequently used for crop and turf irrigation
• 99 of pathogens destroyed within 6 hours of
  exposure to oxygen and sunlight
• Wastewater irrigation in public spaces (golf
  courses) require tertiary treatment of water and
  labeling of sprinklers/valves (red cover with
  Non-Potable in English Spanish)

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Ground Water Storage

• Underground lakes rivers? No!
• Pore spaces between individual particles (sand
  and gravel)
• Fractures in hard rock
• Porous sandstone
• Solution channels or caverns in limestone or
  gypsum (nearly underground rivers)

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Ground Water Movement

• Movement rate is typically tenths of a foot per
  day up to a few feet per day
• Rate is dependent on
• the size and number of openings (pore spaces,
  fractures, solution channels)
• the amount of water pressure created by
  differences in water levels

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Ground Water Terminology

• Porosity percentage of a geologic formation
  that consists of open spaces (same as soil
  porosity)
• Specific yield percentage of a formation that
  is occupied by water which will drain out by
  gravity
• Specific retention percentage of the formation
  that is occupied by water which is retained
  against gravity
• Specific retention Specific yield Porosity
• Permeability property of formations indicating
  how rapidly water will be transmitted (high in
  sands and gravels low in clays)

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Ground Water Terminology 2

• Saturated zones portions of a soil profile or
  geologic formation where all spaces or voids are
  filled with water (no air is present)
• Unsaturated zones soil and geologic materials
  located between the land surface and the
  saturated zone (spaces or voids are filled with
  combination of air/water)
• Water table level in a formation below which
  all spaces or voids are filled with water (top of
  the saturated zone)

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Ground Water Terminology 3

• Aquifer saturated formation that will yield
  usable quantities of water to a well or spring
• Unconfined aquifer (water table aquifer)
  aquifer whose upper water surface is the water
  table (no layers restricting water movement into
  the saturated zone from above)
• Confined aquifer (artesian aquifer) aquifer in
  which the water is confined under pressure
  between low-permeability materials (aquitards)

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Confined and Unconfined Aquifers
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Well Drilling

• Dug wells dug by hand or backhoe equipment
• Driven Wells sand point wells are driven with a
  sledge hammer or post driver
• Dug Driven wells are shallow, low yielding
  wells
• Professionally Drilled Wells  
• Cable-tool percussion wells a heavy bit is
  repeatedly lifted and dropped to loosen and
  break-up formation
• particles are periodically removed with a bailer
• effective for formations containing rocks and
  boulders
• generally for wells 12 inches in diameter or less

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Well Drilling 2

• Rotary rotating bit connected to a hollow drill
  stem through which drilling fluid is pumped
• Drilling fluid serves several purposes
• Cools lubricates the drill bit
• Removes drill cuttings
• Different rotary versions
• Direct rotary fluid down stem, up the borehole
• Reverse rotary fluid down borehole, up drill
  stem
• Air rotary compressed air is the drilling fluid

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Well Components

• Bore hole cylindrical shaped opening created by
  the drilling operation
• Casing round pipe (usually steel) that protects
  the bore hole from collapse and houses the pump
• Screen (intake section) manufactured screens
  are best, but other types of perforations are
  sometimes used (torch slots, saw cuts, etc.) 
• Gravel pack (optional) material with greater
  permeability placed around intake section 

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Well Hydraulics Terminology

• Static water level water level in a well when
  the pump is not operating (is idle for several
  days)
• Pumping water level water level in a well when
  the pump is operating at some flow rate
• Drawdown difference between water levels in a
  well under non-pumping and pumping conditions
• Cone of depression drop in ground water levels
  around a well or group of wells in response to
  ground water withdrawal aquifer volume that is
  affected by pumped well(s)
• Lift vertical distance from the water level in
  a well during pumping to some delivery point

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Well Hydraulics Terminology
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Well Yield

• Influencing factors
• aquifer characteristics
• strainer characteristics (screen, gravel pack,
  etc.)
• well penetration depth into the aquifer
• well diameter (doubling d results in about a 10
  increase in Q)
• Yield Q and drawdown H-h
• Interrelated (Q increases as H-h increases)
• Case of diminishing returns (maximum practical Q
  occurs when H-h 0.88H)

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Test Holes

• Is a well feasible?
• Where should it be located?
• Usually rotary drilled about 4-inch diameter
• Things you can learn
• depth to static water level
• type and thickness of water-bearing formations
• best methods for drilling and developing the well
• recommended gravel pack, screen size, etc.

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Characteristics of Aquifer Materials
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Hydraulic Conductivity of Aquifer Materials
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Radius of Influence in Aquifer Materials
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Gravel Pack

• Gravel pack (envelope) coarse particles placed
  between the aquifer material and the well screen
• Material should be rounded, silica gravel
• Gravel pack purposes
• keep fine sand from entering the well
• increase permeability around the screen
• allow larger openings in the screen

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Well Screens

• Screen types 
• Home-made torch cuts mill/sawed slots (not
  good)
• Manufactured shutter/louver type, continuous
  slot (V-shaped or round wire)
• Length depends on aquifer formations
• Lower 1/3 of unconfined aquifer depth
• 80-90 of confined aquifer thickness
• Slot width size to exclude 90 of gravel pack or
  aquifer material (if the well is gravel packed)
• Diameter depends on well size also entrance
  velocity considerations
• Type of material strength, corrosion,
  incrustation factors

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Torch-cut slots in a steel casing Torch-cut slots
normally result in about 10 open area for water
flow.
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Manufactured Well Screens
Stainless Steel Galvanized Steel
Large Screen Opening Small Screen Opening
Water Flow Direction
Triangular X-section Round X-section
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Screen Sizes and Materials
8-inch Galvanized Steel 6-inch Bronze 4-inch St
ainless Steel
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16-inch Diameter Carbon Steel Johnson Agri-Screen
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Well Development

• Purposes
• Remove skin resulting from drilling mud
• Increase permeability around the well
• Stabilize formation to minimize sand pumping
• Methods
• Bailing (with drillers bailer)
• Intermittent pumping (rapid pump on/off cycles)
• Surging (with surge block piston)
• Jetting (high pressure water streams)
• Others- surfactants, dry ice, etc. 

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Test Pumping

• Purposes
• determine well performance
• help in pump selection
• Procedures
• Pump at constant rate for period of time measure
  Q and drawdown
• Step tests (different flow rates)
• Start at 10 of est. max. yield measure Q
  drawdown
• Increase flow rate repeat Q drawdown
  measurements

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600 gpm/60 ft 10 gpm/ft
60 ft
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Irrigation Water Quality

• Sediment suspended sand, silt and clay
• Total salinity dissolved mineral salts
• Sodicity sodium content of dissolved minerals
• Toxic minerals boron, chlorides, etc.

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Sediment

• Sediment suspended sand, silt and clay
• Effects
• emitter clogging
• nozzle wear and clogging
• capacity of canals, reservoirs, pipelines reduced
• Control
• large particles- sediment basins, cyclonic
  separators
• small particles- filters, flocculation/filtration

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Salinity

• Concentration of Total Dissolved Solids (TDS)
• Units milligrams/liter (mg/L) or parts per
  million (ppm)
• 1mg/l 1 ppm
• Electrical Conductivity (EC)
• Units deciSiemens per meter (dS/m)
• 1 dS/m 1 millimho/cm 1000 micromhos/cm
• Approximate relationship TDS 640 (EC)
  where TDS is in mg/L and EC is in dS/m
• Commonly measure ECe (EC of the extract
  taken from a saturated soil)

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Causes of Salinity

• All soils and irrigation waters contain salt
• ET tends to increase salt concentrations
• In humid regions, rainfall provides dilution and
  flushing below the root zone
• In arid regions, salts tend to concentrate much
  more over time, especially at the soil surface 

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Salinity Effects

• Reduced water availability to plants (osmotic
  effect)
• ?T ?M?G?O
• More difficult for roots to extract water from
  the soil because increased osmotic potential
  raises total water potential the plant must
  generate to extract water from the soil

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Salinity and Soil Water Potential
Salt Concentrations 0.1 1000 mg/l 0.2
2000 mg/l 0.3 3000 mg/l 0.4 4000 mg/l
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Salinity Effects Part 2

• Yield impacts depend on the soil salinity level
  and the crop's sensitivity to it
• Yr 100 for ECe lt T
• Yr 100 - S (ECe - T) for ECe gt T (Eq.
  6.4)
• Yr relative yield, ()
• T threshold salinity where yield is first
  reduced, (dS/m)
• S slope of yield-salinity relationship, (/dS/m)
• Minimum value for Yr is 0

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Threshold, T, and Slope, S, Salinity Values
S
1 dS/m
T
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Irrigation Water QualityTurf
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Sodicity

• Sodicity sodium level in water or soil,
  particularly in relation to the levels of calcium
  and magnesium
• Effects
• Clay particles swell and aggregates disperse
  (soil structure)
• Reduced infiltration and percolation
• Poor tilth and aeration
• Slick spots (Black alkali soils)
• (when calcium and magnesium dominate, soil
  structure is much better)

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Sodicity Measurement

• Sodium Adsorption Ratio (SAR)
•  
•  
• C's have units of moles of charge per cubic meter
  (meq/L ? valence)

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Potential for infiltration problems due to high
Na water.
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Potential for infiltration problems due to high
Na water.
EC 0.40 mmho/cm SAR 8.2
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Mineral Toxicity

• Plant damage resulting from the uptake and
  accumulation of certain ions
• Examples boron, chloride, sodium
• Evidence of toxicity usually appears as burning
  on margins of mature leaves
• Generally not a problem with most irrigation
  waters 

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Leaching

• Leaching Addition of excess water which will
  wash accumulated salts below the root zone
• Occurs naturally in humid regions due to heavy
  rainfall
• Artificial leaching in arid regions through over-
  irrigation
• Either method requires good drainage

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Leaching Fraction, L
L Dd/Di Ci/Cd ECi/ECd L Leaching
fraction D Water depth C Water mineral
concentration (TDS) EC Water electrical
conductivity i Irrigation water (consistent
units in/in, d Drainage water ppm/ppm,
dS/m/dS/m)
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Leaching Requirement, Lr
Lr Leaching requirement (i.e., the
leaching fraction required) There are simple
models which estimate the amount of leaching
required to maintain an acceptable level of soil
salinity, based on a linear distribution of
accumulated salts in the root zone.
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Leaching Requirement as a function of ECi and T
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Lr when ECi 2.40 dS/m and T 2.5 dS/m
Lr 0.17
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Reclamation of Saline Soils

• Salinity
• Natural leaching with rainfall
• Artificial leaching with excess irrigation
• Good drainage through root zone required
• Sodicity
• Addition of soil amendments (Calcium)
• Reclamation should be done whenever salt levels
  reach an economic threshold (Crop yield is
  significantly affected)

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Water Law

• Riparian Doctrine "a landowner contiguous to a
  stream is entitled to have water of the stream
  flow by his/her land undiminished in quantity and
  unpolluted in quality"
• Based on English common law
• Ground water context ownership of overlying
  land
• Doctrine is often modified to the concept of
  "reasonable use"
• (Prior) Appropriation Doctrine "diverting water
  and putting it to a beneficial use creates a
  water right"
• Early miners' claims "first in time is first in
  right" 

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Beneficial Uses

• Domestic
• Industrial
• Irrigation
• Livestock
• Power generation
• Recreation
• Aquatic life

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Water Rights (cornerstone of the Appropriation
Doctrine)

• Water is owned by the public
• State can grant the right to use water
• Certain quantity, certain use, certain point of
  diversion
• Priority is very important (senior vs. junior
  rights)
• Can be bought and sold
• No guarantee of water
• Non-use forfeits the right
• Normally administered through a permit system

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26 million Water Rights Ruling Scrutinized  SAN
DIEGO A 26 million judgment against the
federal government, which was awarded to a group
of California farmers for a 1990s water
diversion, is being questioned by
environmentalists, The Associated Press (AP) said
in an article reported by The Mercury News.A
federal judge ruled in December that the farmers
were entitled to compensation for the water they
lost. If the judgment survives expected legal
challenges, the government could find itself
forced to pay millions more for efforts to
protect endangered fish, the article said.That
instance would have implications across the West,
according to the paper. Along the
California-Oregon border, for example, a similar
court case could leave the government with a 100
million bill for water diverted from farmers in
2001 for species protection.In the first
decision of its kind, Senior Judge John Wiese
ruled that the government's halting of water
constituted a "taking" or intrusion on the
farmers' private property rights. The Fifth
Amendment to the Constitution prohibits the
government from taking private property without
fair payment.
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Oklahoma Water Rights

• Combination of Riparian and Appropriation
  Doctrines (like most western US states)
• Owning land over groundwater or by a stream
  grants domestic use by Riparian Doctrine
• Household use
• Irrigate 3 acres or less (for any purpose)
• Water free range livestock at normal stocking
  rate
• All other uses require a permit under
  Appropriation Doctrine (OK Water Resources
  Board)