Table 2

Table 2. Directions of change in major indicator variables predicted by GCM for several water management options. Symbols are as follows: positive impact of a policy (+); negative impact (-); and gross uncertainty (?), i.e., the model prediction can go either way depending on uncertain quantitative parameter values. More extreme changes and uncertainties are shown by multiple signs. Time scale (in years) to complete major transient change is shown in parentheses.

	Policy option
Response indicator	Optimize flows for power production	Eliminate diurnal flow variation, allow seasonal changes	Seasonally adjusted steady flows^a	Beach/habitat- building flows	Warmwater release from GCD^b	Warmwater release plus turbidity addition at GCD
Delivered power cost to ratepayers	-- (0)	+ (0)	++ (0)	0/+ (0)	++ (0)	+++ (0)
Sand beach area (campsites and vegetation)	+ (0.5)	-- (1-3)	? (1-3)	++ (0)		+ (1-3)
Main system sand storage	- (5)	+ (5)	-- (3-5)	- (0)		++ (1-3)
Autochthonous primary production	-- (0.1)	+ (0.5)	- (1-2)	+ (0)	-? (1)	--- (0.1)
Riparian plant and insect production	-- (1)	- (5)	-- (2-10)	- (0)		+ (5)
Aquatic insect production	-- (0.5)	+ (1)	-- (2)	- (0)	-? (2)	--- (0.5)
Backwater habitat productivity	? (1-10)	? (10-20)	? (1-20)	(0)		? (1-20)
Trout fishery	- (3)	+ (5)	-- (5)	- (5)	-- (3)	--- (0.5)
Warmwater exotic fishes	-- (5)	?? (5)	?? (5-10)	? (5-10)	?? (10)	?? (10)
Humpback chub	? (15)	? (15)	? (15)	? (15)	? (15)	? (15)
Native suckers (flannelmouth, bluehead)	?? (15-25)	?? (15-25)	?? (15-25)	? (15-25)	?? (15-25)	?? (15-25)
Riparian birds (waterfowl, Peregrine Falcon)	- (5-10)	+ (5)	- (10)	? (10)	-? (10)	--- (10)

^a Seasonally adjusted steady flows remove diurnal variation, have spring-summer peaking, and relatively low winter flow in order to move toward a more natural seasonal hydropattern.

^b Assumes the capability to release warm Lake Powell surface waters for 2-3 months/year.