Colloff et al. Evaporation from irrigation dams and channels in the northern Murray-Darling Basin
We mapped and quantified 2,786 storages and 10,173 km of irrigation channels and estimated the amount of water lost each year to evaporation.
Methods: we mapped all on-farm storages in cotton-growing catchments in the northern Murray-Darling Basin using Goofle Earth Pro, calculated areas and volumes (based on Lidar data) and copiled a database, including year of contrruction so we could estimate cumulative growth in storage numbers and capacity over time. To estimate rates of evaporation from storages and channels, we downloaded the time series of the percentage of surface area observed as wet (i.e. holding water) from the Digital Earth Australia website, converted it to an Excel spreadsheet, coded dates of observation by month, recorded number of days between observations and converted the percentage area wet into hectares. We deleted dates with no data due to cloud cover. For each observation we recorded daily evaporation, expressed as the monthly mean, from the nearest weather station where pan evaporation was recorded. We applied a correction factor of x0.75 to account for higher evaporation from a Class A Pan caused by solar heating of its metal surfaces. We multiplied the area of each storage observed as wet by the number of days this area was recorded and multiplied the product by the mean monthly rate of evaporation to obtain the number of hectares to a depth of 1 mm. We converted this area to volume of evaporation (in megalitres) by multiplying by 0.01 (where 1 ha of 1 mm depth = 10,000 L or 0.01 ML). We summed the volume of evaporation for each water year (July-June) and estimated the total annual volume of evaporation and the mean and total volume over the lifetime of the storage. To estimate mean annual volume of evaporation for each catchment or sub-catchment, we calculated annual volume of evaporation from a representative sample of storages (n = 414; 14.9% of 2,786 storages), constructed a calibration curve of storage area v. evaporation and used the regression equation for the line of best fit to calculate evaporation for the other storages.To estimate total evaporation for each sub-catchment and catchment over time, we used data on annual evaporation for each storage in the representative sample and divided it by storage area to obtain the annual rate of evaporation per hectare of storage. We then calculated the mean for all storages for each year and multiplied this by total area of storages in the catchment for that year. We estimated annual volume of evaporation from major irrigation channels (i.e. that held water most of the time, linked to the main channel, other storages or extended from storages onto paddocks). We excluded minor channels that contained water only during the growing season. Channels were traced onto topographic maps and their length measured. We used Google Earth Pro to check they were major channels containing water and determine mean width (n = 10 per sub-catchment or catchmen). Total channel area was calculated and evaporation estimated based on mean annual rate for each sub-catchment and catchment (Table S1). Channel capacity was calculated from the area and an estimate of mean depth of 1.5 m.
Results: annual mean total evaporation was 1,203 GL (969 GL from storages, 234 GL from irrigation channels), representing 38% of the mean annual surface water take from the cotton-producing catchments. On-farm storages covered 94,632 hectares, with a capacity of 3,296 GL; an exponential increase since 1995 when a cap on irrigation diversions was introduced. Storages contained water for 89% of the time and were full or near-full 31% of the time. If evaporation from storages and channels is taken into account, it takes an average of 11.8 ML to grow a hectare of cotton: almost twice that claimed by the cottton industry.
Type
collection
Title
Colloff et al. Evaporation from irrigation dams and channels in the northern Murray-Darling Basin
Collection Type
Dataset
Access Privileges
Fenner School of Environment & Society
DOI - Digital Object Identifier
10.25911/f66w-z070
Metadata Language
English
Data Language
English
Significance Statement
Estmates of annual mean evaporation from large on-farm storages in cotton-growing catchments of the northern Murray-Darling Basin. First estimate made. Includes cumulative rates of evaporation with increases in storage numbers and capacity since 1984.
Full Description
We mapped and quantified 2,786 storages and 10,173 km of irrigation channels and estimated the amount of water lost each year to evaporation.
Methods: we mapped all on-farm storages in cotton-growing catchments in the northern Murray-Darling Basin using Goofle Earth Pro, calculated areas and volumes (based on Lidar data) and copiled a database, including year of contrruction so we could estimate cumulative growth in storage numbers and capacity over time. To estimate rates of evaporation from storages and channels, we downloaded the time series of the percentage of surface area observed as wet (i.e. holding water) from the Digital Earth Australia website, converted it to an Excel spreadsheet, coded dates of observation by month, recorded number of days between observations and converted the percentage area wet into hectares. We deleted dates with no data due to cloud cover. For each observation we recorded daily evaporation, expressed as the monthly mean, from the nearest weather station where pan evaporation was recorded. We applied a correction factor of x0.75 to account for higher evaporation from a Class A Pan caused by solar heating of its metal surfaces. We multiplied the area of each storage observed as wet by the number of days this area was recorded and multiplied the product by the mean monthly rate of evaporation to obtain the number of hectares to a depth of 1 mm. We converted this area to volume of evaporation (in megalitres) by multiplying by 0.01 (where 1 ha of 1 mm depth = 10,000 L or 0.01 ML). We summed the volume of evaporation for each water year (July-June) and estimated the total annual volume of evaporation and the mean and total volume over the lifetime of the storage. To estimate mean annual volume of evaporation for each catchment or sub-catchment, we calculated annual volume of evaporation from a representative sample of storages (n = 414; 14.9% of 2,786 storages), constructed a calibration curve of storage area v. evaporation and used the regression equation for the line of best fit to calculate evaporation for the other storages.To estimate total evaporation for each sub-catchment and catchment over time, we used data on annual evaporation for each storage in the representative sample and divided it by storage area to obtain the annual rate of evaporation per hectare of storage. We then calculated the mean for all storages for each year and multiplied this by total area of storages in the catchment for that year. We estimated annual volume of evaporation from major irrigation channels (i.e. that held water most of the time, linked to the main channel, other storages or extended from storages onto paddocks). We excluded minor channels that contained water only during the growing season. Channels were traced onto topographic maps and their length measured. We used Google Earth Pro to check they were major channels containing water and determine mean width (n = 10 per sub-catchment or catchmen). Total channel area was calculated and evaporation estimated based on mean annual rate for each sub-catchment and catchment (Table S1). Channel capacity was calculated from the area and an estimate of mean depth of 1.5 m.
Results: annual mean total evaporation was 1,203 GL (969 GL from storages, 234 GL from irrigation channels), representing 38% of the mean annual surface water take from the cotton-producing catchments. On-farm storages covered 94,632 hectares, with a capacity of 3,296 GL; an exponential increase since 1995 when a cap on irrigation diversions was introduced. Storages contained water for 89% of the time and were full or near-full 31% of the time. If evaporation from storages and channels is taken into account, it takes an average of 11.8 ML to grow a hectare of cotton: almost twice that claimed by the cottton industry.
Contact Email
Matthew.Colloff@anu.edu.au
Contact Address
Fenner School of Environment and Society,
Australian National University,
Bldg. 141, Linnaeus Way, Canberra, ACT 2601
Contact Phone Number
0458683231
Principal Investigator
Matthew Colloff
Fields of Research
300201 - Agricultural hydrology
Socio-Economic Objective
280111 - Expanding knowledge in the environmental sciences
Keywords
floodplain harvesting;
irrigation diversions;
river flows;
Murray–Darling Basin Plan;
water policy reform;
water accounting;
management of evaporation
Type of Research Activity
Applied Research
Date Coverage
1984
2024
Geospatial Location
text
northern Murray-Darling Basin
Year of data publication
2025
Creator(s) for Citation
Matthew
Colloff
Publisher for Citation
The Australian National University Data Commons
Access Rights
Open access allowed
Access Rights Type
Open
Rights held in and over the data
CC BY
Licence Type
CC-BY - Attribution
Retention Period
Indefinitely
Extent or Quantity
419
Data Size
22,0000 KB
Data Management Plan
No
Status: Published
Published to:
Published to:
- Australian National University
- Australian National Data Service
Related items
- hasAssociationWith:
Dr. Matthew Colloff [anudc:6336] - hasPrincipalInvestigator:
Dr. Matthew Colloff [anudc:6336]