The Colorado River is the most important source of water in the arid southwest but current allocations among the states and Mexico are based on flows estimated from less than 80 years of direct measurement. Are these historic flows representative of the flows that can be expected in the future? Have there been times when the river's flow was much less than flows directly observed? Has the seasonality of the river's flow varied during the past 2,000 years? To answer these questions, we need records covering longer time periods than are provided by direct measurements.
Information on the duration and magnitude of times of low flow is critical for planning allocations during future droughts. The frequency, duration and magnitude of times of low flow in the past provide estimates of the likelihood, duration and magnitude of low flow in the future. Results of this study will be of interest to international (U.S.-Mexico), federal, regional, state, and district level agencies concerned with allocating future supplies of Colorado River water.
We will provide estimates of the flow of the Colorado River where it enters the northern Gulf of California. Isotopic analyses of well-dated mollusks will provide estimates of the volume of river water entering the Colorado Delta in 50 year intervals back to the year A. D. 1. Isotopic analyses of growth bands within shells will provide estimates of the seasonality of flow during the past 2,000 years.
These estimates will also be used to corroborate tree-ring estimates of flow during the past 450 years and to identify the likely recurrence of times of unusually high or low flow conditions. Such information can be used in developing plans for managing the Colorado River system in times of water shortage.
Not satisfied to pass a quiet day after the labors of the week, many
of the men, seduced by the enticing weather and smooth water, started in
a boat after breakfast on a clamming excursion towards the Gulf. A furious
northwester set in about noon, and continued till dark, occasioning us
a good deal of anxiety for the safety of the clam hunters... They had been
caught in the gale, and were exhausted with rowing and bailing. They had
not got any clams, but were hungry, wet, and bedraggled, and quite satisfied
that it was useless to search for either pleasure or shellfish at the mouth
of the Colorado.
--Lieutenant Joseph C. Ives, Corps of Topographical Engineers, December
6, 1857
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