aquifer. Pumping out of the aquifer creates a deficit that the river will eventually recharge. A
major complication is that the recharge process may take decades. But the net effect is that the
river is drawn down as it replenishes the depleted aquifers. This affects downstream surface
users and compact obligations. To counteract the effect on surface flows, often the SEO will
require junior groundwater users to purchase senior surface water rights to neutralize the effect
on the river. We have not implemented this part of the law either - witness the Pecos river valley.
The state of New Mexico has been spending millions of dollars in buying or leasing water to
meet Compact obligations to Texas caused by excessive groundwater pumping. In essence the
state of New Mexico is buying out Pecos valley agriculture to ship water to Texas (just a side
note, by the time the water in the Pecos reaches the New Mexico/Texas border it is too salty to
be of any value).
A Lower Pecos Valley Regional Water Plan approved by the NM Interstate Streams
Commission in 2002 has an innovative method to meet compact obligations. Junior groundwater
irrigators in a water short year would pump out of the aquifer directly into the river enough water
to meet compact obligations. In water surplus years, the river would naturally replenish the
depleted aquifers and still satisfy compact obligations and senior water rights. The junior water
right holders would bear the cost of the program, but this would be small price considering the
alternative, a shut down of groundwater based agricultural production.
Anther conjunctive relationship between river and shallow aquifers is return flow.
Irrigators put on more water than is actually required by the crop. This is necessary even with
very efficient irrigation. The evapotranspiration process of the crops builds up salts in the root
zone. Sufficient salt buildup will reduce yields or worse kill the crop. Using leaching fractions, a
technique of putting on more water that the crop uses and leaching the salt down below the root