There have been ongoing negotiations for several years directed at developing the new Colorado River management guidelines that will go into place in 2026 when the 2007 interim guidelines expire.
The goal of negotiations among the seven U.S. Colorado River basin states has been to submit a single document proposing guidelines to the Bureau of Reclamation (BoR) within the U.S. Department of the Interior. However, the upper and lower basin state groups have been dealing with significant differences and were not able to come to a consensus agreement. As a result, the upper and lower basin delegations each submitted separate proposals to the BoR in early March.
Both proposals are under review by the BoR officials who have indicated that they will be working with the basin states in the next six months to develop a consensus draft proposal for post-2026 river management by the end of 2024.
To help review the differences between the two proposals, I have summarized the basic parameters in Tables 1 through 4 (Davis, 2024a and Hager, 2024a).
To help review the differences between the two proposals, I have summarized the basic parameters in Tables 1 through 4 (Davis, 2024a and Hager, 2024a).
Lower Basin Proposal Summary
Table 1. Outline of lower basin proposal for Colorado River water management based on reservoir levels of Lakes Powell and Mead.
|
Reservoir Levels (%) |
Lower Basin Reductions (MAF/Year)* |
Upper Basin Reductions (MAF/Year) |
|
70 |
0 |
0 |
|
59-69 |
0-1.5** |
0 |
|
39-58 |
1.5 |
0 |
|
≤ 38 |
X |
X |
Note:
*MAF = million acre-feet
**Up to 1.5 MAF/year reductions for the entire lower basin depending on the reservoir levels between 59-69%. Divisions of water reductions among the lower basin states is not specified.
X = 1.5-3.9 MAF/year total reductions for the total Colorado River system. The specific amounts of water reductions in each of the upper and lower basins with reservoir levels at 38% or less are not specified in the current lower basin proposal.
Table 2. Annual reductions in Colorado River water allocations for the lower basin states when the reservoir water levels are between 39-58% in both reservoirs, based on the lower basin proposal.
|
Lower Basin State |
Reduction (acre-feet) |
|
Arizona |
760,000 |
|
California |
440,000 |
|
Nevada |
50,000 |
|
Mexico* |
250,000 |
*Contingent upon Mexico’s agreement with the reductions.
Based on the lower basin proposal, reservoir levels at 38% of capacity and lower would result in reductions from 1.5 to 3.9 MAF/year, depending on the levels of water depletion in Lakes Powell and Mead. The exact splits in water reductions between the upper and lower basins in this range of reservoir depletion is not specified in the lower basin plan, at least based on the materials used for this review. Accordingly, the share of water reductions that Arizona and California would take are not specified either.
For reservoir levels of less than or equal to 38%, the cuts would gradually tighten until the reservoirs fall below 23% of capacity. At that point, all Colorado River basin states would have to take maximum collective reductions of 3.9 million acre-feet a year.
Upper Basin Proposal Summary
Table 3. Outline of reductions in water releases from Lake Mead based on the upper basin proposal.
|
% of Capacity |
Release Reductions (MAF/year)* |
|
90 |
0 |
|
70-90 |
0-1.5 |
|
20-70 |
1.5 |
|
≤ 20 |
1.5-3.9 |
*MAF = million acre-feet
Specifically for Lake Mead, the Upper basin states proposal includes points:
— If Mead is at least 90% full, the Lower Basin states would take no cuts in their supplies.
— If Mead is between 70% and 90% full, the Lower Basin states would lose up to 1.5 million acre-feet per year.
— If Mead is 20% to 70% full, Lower Basin states would lose 1.5 million acre feet a year.
— If Mead is 20% full or lower, Lower Basin states would have to take cuts of up to 2.4 million acre-feet on top of the 1.5 million they’re already taking.
For Lake Powell, the Upper Basin states proposed a series of shrinking water releases depending on the lake’s elevation:
— If Powell is 81% to 100% full, the lake will release anywhere from 8.1 to 9 million acre-feet of water annually to send to Lake Mead for use by Lower Basin states.
— If Powell stands anywhere from 20% of 81% full, the lake will release somewhere between 6 million and 8.1 million acre-feet a year to Mead.
— If Powell is less than 20% full, it will send to Mead 6 million acre-feet a year.
Table 4. Outline of water releases from Lake Powell based on the upper basin proposal.
|
% of Capacity |
Lake Powell Water Release (MAF/year)* |
|
81-100 |
8.1-9 |
|
20-80 |
6.0-8.1 |
|
< 20 |
6.0 |
*MAF = million acre-feet
It is important to note that the upper basin proposal puts the entire reduction of Colorado River water use on the lower basin states. Essentially, the upper basin states see the need for Colorado River water reductions as lower basin responsibility entirely.
To help keep the conversation interesting, the Gila River Indian Community (GRIC) Governor Stephen Roe Lewis announced on 13 March 2024 at the University of Arizona Water Resource Research Center Annual Conference in Tucson, Arizona (WRRC, 2024) that their community is opposed to the lower basin proposal and with a letter to the BoR, GRIC is seeking to reinforce their existing rights to water and gain a stronger place and voice in the negotiations regarding future access to Colorado River water via the Central Arizona Project (CAP). Sixteen other tribes in the Colorado River basin signed the 11 March letter from GRIC to the BoR. Eight of those tribes are from Arizona (Davis, 2024b and Hager, 2024b).
The GRIC and some other tribes are pushing for the BoR to find other supplies of water to replace any water that is cut from CAP deliveries or provide financial compensation, particularly to cover existing and/or potential tribal water rights for Colorado River water.
There are many interesting ramifications that are possible from these recent developments. The BoR has two proposals to review from the upper and lower basins and now the added dimension of the GRIC opposition. These recent requests from GRIC and some other tribes will need to be taken into consideration along with the proposal elements from both the upper and lower basins.
References
Davis, Tony. 2024a. States are far apart on new Colorado River water-saving plans sent to U.S. agency. Arizona Daily Star, 13 March 2024.
At events and in the halls of the Yuma Agricultural Center, I’ve been hearing murmurings predicting a wet winter this year…
As the Yuma Sun reported last week, “The storms of Monday, Aug. 25 [2025], were the severest conditions of monsoon season so far this year in Yuma County, bringing record-rainfall, widespread power outages and--in the fields--disruptions in planting schedules.”
While the Climate Prediction Center of the National Weather Service maintains its prediction of below average rainfall this fall and winter as a whole, the NWS is saying this week will bring several chances of scattered storms.
These unusually wet conditions at germination can favor seedling disease development. Please be on the lookout for seedling disease in all crops as we begin the fall planting season. Most often the many fungal and oomycete pathogens that cause seedling disease strike before or soon after seedlings emerge, causing what we call damping-off. These common soilborne diseases can quickly kill germinating seeds and young plants and leave stands looking patchy or empty. Early symptoms include poor germination, water-soaked or severely discolored lesions near the soil line, and sudden seedling collapse followed by desiccation.
It is important to note that oomycete and fungal pathogens typically cannot be controlled by the same fungicidal mode of action. That is why an accurate diagnosis is critical before considering treatments with fungicides. If you suspect you have seedling diseases in your field, please submit samples to the Yuma Plant Health Clinic or schedule a field visit with me.
National Weather Service Climate Prediction Center: https://www.cpc.ncep.noaa.gov/
National Weather Service forecast: https://forecast.weather.govDue a lack of effective post-emergence herbicides, most vegetable crops are hand weeded following cultivation to remove in-row weeds. This operation is costly and finding labor to perform the task has become increasingly difficult. Precision micro-sprayers for delivering herbicides have been developed, but lack sufficient speed, accuracy and off-target spray control to be commercially viable. To address this, a high speed, centimeter scale resolution sprayer that can spot apply herbicides to weeds with minimal off-target spray while traveling speeds that are viable for commercial farming operations was developed. The objective of this research was to evaluate the performance of the device in terms of spray delivery accuracy, off-target spray quantity, weed control efficacy and crop safety. The spray assembly comprised 12 custom-built spray modules spaced 1 cm apart. The device was tested with lettuce in the laboratory at a travel speed on 2.0 mph while targeting three weed species at three stages of growth. Results showed that targeting accuracy of spray delivered was ± 2 mm and that the percentage of off-target spray was less than 3%. Weed control efficacy exceeded 95% and there was no observable crop injury. Improvements to the original design were identified and the enhanced sprayer was found to provide sub-centimeter precision. Practical applications of the technologies developed include precision spot spraying of weeds in lettuce, carrot, onion, spring mix and other vegetable crops. A remaining technical challenge for the realization of an automated precision weeding machine is the development of a camera imaging system capable of reliable crop/weed differentiation. Field testing of the precision spot sprayers is also needed.
Click the following link to watch presentation on Centimeter Scale Resolution Spot Sprayer.
https://www.youtube.com/watch?v=XBNGsIu27K0
Burndown herbicides are used to kill emerged weeds prior to planting lettuce. Some of the species we have are very hard to kill. Therefore, these weeds would have to be controlled using selective herbicides after the crop has emerged.
Some of the products we have available are glyphosate (Roundup), paraquat (Gramoxone), oxyfluorfen (GoalTender), carfentrazone (Aim,Shark), Pyraflufen (ET), and pelargonic acid (Scythe). There are other products that are being developed such as the S3100 from Valent USA.
Herbicides that can be used up to just before crop emergence are Roundup, Paraquat and Scythe, these provide no residual weed control. ET has an interval of 1 day following preplant burndown application for leafy vegetables. AIM herbicide also requires for some crops (tobacco) 1 day following preplant burndown1. Oxyfluorfen does not bind strongly to soil but stays active for a long time and requires ninety days after application for the low rate and 120 days for the high rate prior to planting lettuce4. It forms a layer on the soil surface that weeds contact as they emerge. If this barrier is destroyed by machinery traffic weeds will not be controlled.
Roundup is a systemic and with a Koc (sorption coefficient) factor of 24,000 adheres very strongly to the soil. So, it is active only on growing plants, but once its bind to the soil is inactive.
Paraquat also adheres good to the soil with a Koc of 1,000,000, so coverage is important for best weed control.
There is a project through the IR-4 program to add the use of glufosinate as a Pre-Plant burndown on spinach, lettuce, broccoli, cabbage, and mustard greens. Hopefully this addition to the label will provide a new tool for our growers in Arizona and other States3
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: CEW moth counts down in most over the last month, but increased activity in Wellton and Tacna in the past week; above average for this time of season.
Beet armyworm: Moth trap counts increased in most areas, above average for this time of the year.
Cabbage looper: Moths remain in all traps in the past 2 weeks, and average for this time of the season.
Diamondback moth: Adults decreased to all locations but still remain active in Wellton and the N. Yuma Valley. Overall, below average for January.
Whitefly: Adult movement remains low in all areas, consistent with previous years.
Thrips: Thrips adults movement decreased in past 2 weeks, overall activity below average for January.
Aphids: Winged aphids are still actively moving, but lower in most areas. About average for January.
Leafminers: Adult activity down in most locations, below average for this time of season.
