Saturday, April 11, 2009

Groundwater-surface water subflow case in the Verde Valley

A suit by Salt River Project against three Verde Valley families over pumping water may be a preview of the debate over the use of river 'subflow' (legally treated as surface water) versus use of groundwater.

Reporter Steve Ayers of the Camp Verde Bugle, has done an admirable job of explaining a complex situation, in light of rulings about statewide adjudication of water rights. [right, Verde River in Verde Valley. Credit, Sedona-Verde Valley Tourism Council]

I thought his descriptions cut right to the key issues:

* Under state law, water in a stream's subflow zone, although flowing underground, beneath and beside the stream channel, is treated the same as surface water flowing in the channel. The rights to surface water are on a "first in use, first in right" basis.
* SRP has argued there is no definitive limit to the depth of the subflow if there is not a clearly defined, non-permeable layer separating the subflow from groundwater.
* In the case of the Verde wells, SRP argues they are drawing from the Verde Formation, a permeable layer of limestone rock beneath the river's subflow, which when drawn from has the effect of drawing down water above it, in the subflow.
* The previous judge in the statewide adjudication case had ruled that all wells located in the subflow of a stream, regardless of depth, were subject to having a surface water right, except those where the owner could prove the water coming from the well was coming from formations below an "impervious formation."

AZGS is currently mapping Holocene-aged units along the Verde River in support of the AZ Dept. of Water Resources for use in the statewide adjudication process. AZGS geologist Joe Cook has covered most of the areas accessible by foot. For the past week, he and fellow geologist Ann Youberg are working along the deeper sections of the river and more remote areas, by raft. We should have photos and details of this most recent work in the next weeks to share with you.

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