Mohave County, USGS present updated forecast showing growing groundwater deficit in Hualapai Valley Basin

Mohave County and the U.S. Geological Survey presented an updated forecast of the Hualapai Valley Groundwater Basin to the Kingman City Council, reporting more irrigated acres in parts of the basin, a larger total water deficit than the 2019 model predicted, and plans for monitoring wells and recharge basins.

The update matters because the basin supplies municipal water for Kingman and agricultural users across the valley; the model informs decisions about monitoring, recharge projects and long-term supply costs. Mohave County and USGS told the council the basin is being depleted faster than it is recharged and that annual updates to the model will continue.

Scott Holtri, Development Services Director for Mohave County, said the county used drone imagery and USGS methods to re‑estimate irrigated acreage across three subbasins and update consumptive‑use projections. The county observed 1,826 acres in the Southern Gregg Subbasin (an increase of about 1,242 acres from 2019), 6,543 acres in the Hualapai Subbasin (about 5,650 fewer acres than 2019), and 8,131 acres in the Kingman Subbasin (about 6,800 more acres than 2019). Holtri said orchard trees comprised roughly 16,122 acres and vines about 383 acres in the survey area, and that orchard water use was modeled at an average 2.72 acre‑feet per acre while vines were modeled at 1.01 acre‑feet per acre.

Using those crop‑type estimates and USGS consumptive‑use factors, the presentation compared the 2019 baseline to 2024 observations. The 2019 observations showed about 14,090 cultivated acres with an estimated demand of roughly 26,060 acre‑feet; the county’s 2024 observations found 16,505 cultivated acres and estimated demand of 44,252 acre‑feet. Holtri said the updated total annual basin deficit is about 50,474 acre‑feet compared with a 2021 estimate of a 30,900 acre‑foot deficit. He added the county estimated natural recharge at about 5,000 acre‑feet per year and incidental recharge at roughly 4,500 acre‑feet per year; previously projected infiltration projects (about 1,200 acre‑feet per year) were not included in the current model because many remain in design.

Holtri explained the Kingman Subbasin is presently about 600 feet below land surface and that model projections show an average depth approaching 1,200 feet around the year 2120. He told the council the Arizona Department of Water Resources regards the 1,200‑foot depth as a water‑adequacy threshold: "The 1,200 foot mark is what ADWR indicates as water adequacy within the state of Arizona. It doesn't mean that we're out of water. What it does mean is that we're probably gonna need to drill further down, and it's gonna be more costly."

Jamie Macey, acting center director for the Arizona Water Science Center at the U.S. Geological Survey, described the model's origins and limitations: "With any model, the data that you have that goes into the model is the limitation. The better the data, the better the model." Macey said USGS provided the modeling tool and that Mohave County staff now insert new data annually to improve forecasts. Macey emphasized that USGS provides science and is not a regulatory agency.

Councilmembers and staff pressed for technical clarifications. Councilmember Staley asked whether the model’s crop‑use values are annual figures; staff confirmed they are annual acre‑feet per acre. On monitoring, county staff said three new groundwater monitoring wells are proposed in the Kingman Subbasin, two to be drilled near 1,100–1,200 feet and one shallower site near the bedrock high that separates subbasins. Macey said monitoring equipment will record water levels every 15 minutes and transmit hourly.

Council members also asked about recharge and data sources. City Manager Walsh said the city has an approved recharge well permitted by ADEQ; pending a few water‑quality adjustments to meet drinking‑water benchmarks, the recharge well could return about 1,000 acre‑feet per year to the Kingman Subbasin. Holtri confirmed that planned city and county recharge volumes are not yet included in the current model runs.

On reporting from farms, staff told the council they recently contacted the Arizona Department of Water Resources and found ADWR had not provided updated farm well reporting data to the county for inclusion in the model. Holtri described the county’s drone and crop‑type approach as conservative: "We're taking, okay, what does it take for that crop to grow, and how much are they growing? And that's the number that we produced." He added the approach is the best available short of metering every well.

The presentation concluded with county and USGS commitments to annual updates to the model, continued monitoring‑well installation, and further work on infiltration projects. No formal council action was taken; the item was a presentation and discussion.

Looking ahead, county and city staff said monitoring wells and infiltration basins are in design, and Mohave County committed to producing the annual update each year to inform Kingman's water planning.