Methodological Inquiry Regarding SWAT Irrigation Efficiency and Manual Irrigation Setup
Chelan
Dear friends and colloquies,
I am currently setting up an irrigation schedule within
the .mgt file
of the SWAT model for irrigated agricultural land. My primary objectives are to
analyze the water footprint and accurately estimate the actual water
abstraction from the source. The irrigation in the study area is conducted
using both surface and subsurface methods.
In the course of this work, I would like to
confirm the status of a known model limitation. Specifically, I recall that a
bug existed in older SWAT versions where the IRR_EFF parameter
was inactive when irrigation was applied manually (as opposed to using the
auto-irrigation routine), meaning it did not properly simulate water losses for
surface irrigation.
My proposed methodology to circumvent this potential issue is as follows:
1. Define the irrigation schedule as Manual Irrigation within the management file.
2.
Set
the irrigation efficiency parameter (IRR_EFF)
to 1.0.
3. Instead of inputting the net irrigation depth, I plan to input the gross irrigation depth (calculated as Net Depth / 0.42, representing the total basin efficiency). This approach aims to ensure that the total water abstracted from the source is accurately represented in the model's water balance.
4. For large irrigation events, I intend to split the total gross depth into multiple, smaller applications scheduled on consecutive days to achieve a more realistic hydrological response from the model.
I would greatly appreciate your expert insights on the following questions:
1. For surface irrigation, when the goal is to calculate actual water abstraction and water footprint, is inputting the gross irrigation depth into SWAT a conceptually sound and valid method? Additionally, what is the threshold (in mm) for a single irrigation application beyond which the model's simulation accuracy might be compromised?
2. Is splitting a single, large irrigation event into two or more sub-events scheduled over consecutive days considered an acceptable and hydrologically reasonable modeling practice within the SWAT framework?
Thank you for your time and consideration of these technical questions. I look forward to your valuable feedback.
Yours sincerely,
Bagher