'Bright line' maps complete for Verde tributaries
VERDE VALLEY - A two-year survey by the Arizona Geological Survey, determining the "bright line" along the Verde River and its tributaries, is complete.
Begun in 2008 at the request of the Arizona Department of Water Resources, the survey delineates the geological structure adjacent to the stream channels called the Holocene floodplain alluvium.
Physically, the Holocene alluvium is nothing more than the sand, gravel and cobble deposited beneath and adjacent to the stream over the last 10,000 years.
Legally, though, its lateral limits constitute the "bright line" that will play a major role in determining whether or not your well is pumping surface water, to which you must have a water right.
"The line makes an assumption as to what is surface water and what is groundwater. If your well is inside the line you are presumed to be pumping surface water," says Duane Wiles, a former judge who now advises the Verde Valley Water Users Association.
The court that is determining all surface water rights in the Gila River watershed, which includes the Verde and its tributaries, has concluded that the lateral limits of the subflow are contained within the Holocene floodplain alluvium.
The depth of the subflow has not been determined and has proven to be a far more complex issue.
The 10 maps released last week do the same thing for Oak Creek, Wet Beaver Creek, West Clear Creek, Fossil Creek and the East Verde River.
Together with the 10 maps of the Verde River released in June, they cover 370 miles of the river and its tributaries and constitute the most complete determination of the river's surface geology done to date.
The survey team used earlier mapping, aerial photography and extensive fieldwork to map the active channel and floodplain deposits as well as terraces, older basin deposits and bedrock.
The maps have been forwarded to ADWR.
"We don't know how this mapping will be applied on the Verde, but the basic data is done and it will be up to DWR and the courts to decide," said project leader Phil Pearthree.