7410

• UCREFRP Catalog Number: 7410
• Author: Williams, O. R., S. L. Ponce and A. E. Johns
• Title: Use of Departure Analysis in Decision Making
• USFW Year: 1988
• USFW - Doc Type: American Water Resources Association
• Copyright Material: YES

H. Recreation and/or Aesthetics.
I. Archaeologic and/or Historic Resources.
J. River Continuum Concept.
K. Habitat Requirements of Virgin Spinedace.

SI.ulation of Hypothetical Hydrologic Regimes

The next step in the Departure Analysis is the simulated perturbation of existing
hydrOlogic regimes. To accomplish this, standard hydrologic and engineering approaches
are employed. Existing formulae and computer models are calibrated and verified with
measured data and then supplied with input data that represent hypothetical alterations
of historic flow regimes.

Examples of alterations include: reduction in non-irrigation season peaks with
associated increases in irrigation season flow, decreased daily flows with periodic
peaks due to peaking hydropower flows, decreased annual or seasonal flows due to
out-of-basin divel:sions, decreases in flow from springs and seeps due to ground water
withdrawals during periods of drought, and increased annual or seasonal flows due to
into-basin diverSions.

~es in Response Variables and CoapariS0D8 With Existing
Conditions of Water-related Resource Variables

The calibrated formulae and models are used to predict changes in selected response
variables (any change from existing conditions is a departure). This information can be
used either to directly describe the effect upon the water-related resource attribute
(e.g., altered low flow regime affects water temperature which affects fish survival) or
to indirectly describe the effect through expert opinion (e.g., experts relate a
simulated increase in sand bars to an increase in exotic plants).

These simulated responses and their associated effects upon water-related resource
attributes are next compared to existing conditions as determined by field measurement
and expert opinion. Changes from the existing condition can be associated with
simulated changes in the hydrologic regime to indicate magnitudes of both the effect and
the perturbation which caused it. By the same token, barometer 'responses can be
identified which presage system responses in instances where hydrologic regime
alterations have occurred or will occur.

SOMKAB.Y

To evaluate the effect of land management decisions which affect numerous
water-related resource values, the NPS has developed, and is using at Zion National
Park, a Departure Analysis. This methodology provides a means for examining the effects
of altered hydrologic regimes upon specific resource values.

With respect to the development of this nations r s water resources, the future is
likely to hold challenges for the NPS. It is evident that any failure to adequately
assess the interactions of hydrologic control _variables and water-related resource
values is likely to visit long-term effects upon the values parks and monmnents were
created to p1;'eserve. With competition for scarce resources increasing, the NPS and
other federal agencies can anticipate a constantly increasing challenge in this area for
some time.

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