irrigation water management

CNMP Development Course November 16-18, 2004

Irrigation Water Management



• Irrigation Water Management is the process of determining and controlling the volume, frequency, and application rate of irrigation water in a planned, efficient manner.


Irrigation Water Management• Why is Irrigation Water Management

Important?– Manage soil moisture to promote desired crop

response.– Optimize the use of available water supplies.– Minimize irrigation induced erosion.– Decrease non-point source pollution of surface

and groundwater resources.– Manage salts in the crop root zone.– Manage air, soil or plant micro-climate.


Irrigation Water Management• Minimum Documentation:

– Crops to be Grown, Cropping Sequence and Soils Information.

– Volume of Water Needed per Irrigation and for the season.

– Application rate of irrigation water.– Records Showing Date and Amount of Water

Applied.• Include type of irrigation scheduling technique used

by the client.– Evaluation of the Irrigation System– Environmental Considerations


Irrigation Water Management• Determining Volume of Water Needed



– Crop Consumptive Use (CU)

The amount of water used by the crop in transpiration and building of plant tissue, and that evaporated from adjacent soil or intercepted by plant foliage. It is expressed as depth in inches or as volume in acre inches per acre. It can represent the daily, design, monthly, or seasonal quantity of water needed for plant growth. Often referred to as Crop Evapotranspiration (ETc ).



– Net Irrigation Water Requirements (Fn )• Crop Evapotranspiration (ETc ).• Auxiliary water needs such as leaching,

temperature modification and crop quality (Aw ).• Effective precipitation (Pe ).• Groundwater contribution (GW).• Change in soil water content for the period of

consideration (ΔSW).



– Net Irrigation Water Requirements (Fn )

http://www.info.usda.gov/CED/




http://www.wcc.nrcs.usda.gov/nrcsirrig/irrig-mgt-models.html



Crop

Evapotranspiration in Inches

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Corn Silage 0.00 0.00 0.00 0.00 1.22 4.17 7.13 5.91 1.14 0.00 0.00 0.00

Grass Pasture 0.00 0.00 1.46 3.31 4.53 5.24 6.22 5.28 4.02 2.48 0.43 0.00

• Determining Volume of Water Needed– Net Irrigation Water Requirements (Fn )

Crop

Net Irrigation Water Requirements in Inches

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Corn Silage 0.00 0.00 0.00 0.00 0.47 3.62 7.13 5.83 1.06 0.00 0.00 0.00

Grass Pasture 0.00 0.00 0.08 1.57 3.15 4.57 6.22 5.12 3.46 0.87 0.00 0.00



– Net Irrigation Water Requirements (Fn ), Auxiliary Water Needs for Salinity Management

• Soils in arid areas have the potential to become saline or sodic.

• Saline or sodic soils will cause poor seed germination and reduced yields.

• Additional water must be added to soils with a potential to have saline or sodic problems to leach excess salts.

• Where the soluble salt content of wastewater is high enough to cause problems, the wastewater must be diluted with good quality water or applications must be limited.



– Net Irrigation Water Requirements (Fn ), Auxiliary Water Needs for Salinity Management



– Net Irrigation Water Requirements (Fn ), Auxiliary Water Needs for Salinity Management Aw = ETc

(1/Lr – 1)where:

Aw = Auxiliary Water Needs for Salinity Management in inches.

ETc = Seasonal Crop Evapotranspiration in inches.

Lr = Leaching Requirement from Figure 2-33 of the NRCS National Engineering Handbook, Part 623, Chapter 2 - Irrigation Water Requirements.



– Net Irrigation Water Requirements (Fn ), Contribution of Ground Water (GW)




Fn = ETc + Aw – Pe – GW - ΔSWwhere:

ETc = Crop evapotranspiration in inches

Aw = Auxiliary water needs for leaching, temperature modification, crop quality in inches.

Pe = Effective precipitation in inches GW = Estimated contribution from

ground water in inches.ΔSW = Change in soil water content for

the period considered.



– Available Water Capacity of Soils (AWC)



http://soils.usda.gov/

• Determining Volume of Water Needed– Available Water Capacity of Soils (AWC)



http://soildatamart.nrcs.usda.gov/




What depth to use in computing AWC?





Given:Silty Clay Loam SoilSoil Depth = 3 feetAWC = 0.20 in/in from 0 to 24 inches of

soil depth0.10 in/in from 24 to 36 inches of soil depth

Managed Crop Rooting Depth = 4 feet

What is the total plant available soil water capacity for the crop being grown?



Determine total plant available soil water capacity:

Use 3 feet to determine total plant AWC since the soil depth is less than the managed crop rooting depth.AWC = 0.20 in/in x 24 inches = 4.8 inches0.10 in/in x 12 inches = 1.2 inches Total Plant AWC = 6.0 inches




MAD is defined as the percentage of the available soil water that can be depleted between irrigations without serious plant moisture stress. MAD is expressed as:– a percentage of the total Plant Available

Water Capacity (AWC),– a soil-water deficit (SWD) in inches, or– an allowable soil-water tension level.

• Determining Volume of Water Needed– Management Allowed Depletion (MAD)



– Management Allowed Depletion (MAD)



– Net Irrigation Application (Fa ) based on Plant AWC:

Fa =

MAD * Plant AWC 100%where:

Fa = Net Irrigation Application in inches

MAD = Moisture Allowed Depletion in percent(50% for Corn Silage)

Plant AWC = PlantAvailable Water Capacity of soils (6 inches)


Fa = 3 inches


– Net Irrigation Application (Fa ) based on Plant AWC for Corn Silage:

Fa = 50% * 6 inches 100%

– Net Irrigation Application (Fa ) based on Net Irrigation Requirement (Fn ):

Fa = 7.13 inches for Corn Silage Fa = 6.22 inches for Pasture

Use this value



– Irrigation System Capacity Requirements

Q = 453 * A * d f * H

where:Q = flow rate (gpm)A = area (acres)d = gross application depth

(in)f = irrigation frequency

(days)H = hours of operation per

day



– Gross Irrigation Application Requirements

d = FaEa

where:d = Gross application, inchesFa = Net application, inchesEa = Application

efficiency of the irrigation system



– Gross Irrigation Application Requirements



– Gross Irrigation Application RequirementsUse a net irrigation application (Fa ) of 3.00 inches. A traveling big gun irrigator with an application efficiency of 60% will be used to irrigate the Corn Silage and Pasture.

d =3.0 inches x

100%60%

d = 5 inches




Q = 453 * A * d f * H

where:Q = flow rate (gpm)A = area to be irrigated is 40 acresd = gross application depth is 5

inchesf = irrigation frequency (days)H = hours of operation per day



– Irrigation Frequency (f):

where: MAD = Management Allowed Depletion (%).Plant AWC = Plant Available Water Capacity

(inches). Daily ETc = Daily Evapotranspiration or

Consumptive Use for the crop being grown (inches/day).

MAD x Plant AWC

Daily ETc

f =



– Irrigation Frequency (f):where:

MAD = 50% for Corn Silage Plant AWC = 6.0 inches Daily ETc = Daily Evapotranspiration or

Consumptive Use for Corn Silage in inchesDaily ETc

=7.13 inches for July

31 daysDaily ETc = 0.23 in/day

50% x 6.0 inches100% x 0.23 in/dayf =

f = 13 Days




Q = 453 * A * d f * H

where:Q = flow rate (gpm) A = area to be irrigated is 40 acres d = gross application depth is 5.0

inches f = irrigation frequency is 13 daysH = 16 hours of operation per day is

desired by the client.




Q = 453 * 40 acres * 5.0 inches

13 days * 16 hours/dayQ = 436 gpm or 0.97 cfs

Note: The existing or planned irrigation system must be able to supply 436 gpm and irrigate the 40 acres of Corn Silage every 13 days to meet the crop evapotranspiration needs during the peak water use period.




< I = 0.43 in/hr


Irrigation Water Management• Irrigation Scheduling


Irrigation Water Management• Irrigation SchedulingImportant factors to keep in mind when developing a irrigation scheduling tool for a client:

• The scheduling tool must consider information about the crop, soil, climate, irrigation system, water deliveries and management objectives.

• An irrigation scheduling tool needs only be accurate enough to determine how much water to apply and when.

• A good rule of thumb to follow when developing an irrigation scheduling tool is to keep it simple and easy for the client to understand.


Irrigation Water Management• Irrigation Scheduling


Irrigation Water Management• Irrigation System Evaluation



Irrigation system evaluation is the analysis of any irrigation system and management based on measurements taken in the field under normal conditions and management.

There are three levels of irrigation system evaluations that can be performed:

Simplified

Abbreviated

Detailed


Irrigation Water Management• Irrigation System Evaluation There are 3 levels of Irrigation System Evaluations:

Simplified – This type of evaluation provides enough information to the landowner/operator to make management and operation decisions. This evaluation usually takes a few hours to complete.

Abbreviated – This type of evaluation provides enough information for the landowner/operator to make management and operation decisions plus identify any problems with the system. This evaluation takes a half to full day to complete.

Detailed – This type of evaluation provides the landowner/ operator with a report and a comprehensive irrigation system operation and maintenance plan. This evaluation can take up to one to five days to complete.


Irrigation Water Management• Irrigation Water Management Jobsheet


Irrigation Water Management• Learning Exercise

Refer to the packet of materials in your course notebook for the learning exercise.



Thank You!

Bruce WilsonEnvironmental Engineer/PE

Portland, Oregon(503) 414-3076

[email protected]

irrigation water management

Documents