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Table 3. Engineering approaches to management and the associated management goals for operation and modification of Glen Canyon Dam to manipulate conditions along the Colorado River corridor within the Grand Canyon. Management goal Management philosophy Engineering approacb Maximae revenues from power prO- duction Traditional river man.agemenr Maximi.z.e power production at timet of maximum power price NaturaJized ecosystem Manage txining ecosystem in- dudll1g de.irll.ble non-native species Useexi~ting srruauresto manage exi5ting resources Effect on W!Jter uaDsfers Potential negative impacts on present rea-eation Results from this approach Power production potential Constraints on power opC2"ariops None; unHmited load.following native fish parasites, are well estab- lished and widely distributed. Only eradication of non-native species on a regional scale, which is highly con- troversial and infeasible atthe present time, might permit full restoration. Removal of the Hoover Dam, lo- cated downstream from the Grand Canyon, mighr also be necessary to restore the full migration potential for wide-ranging fish species, such as the Colorado squawfish and the razorback sucker. Attempts at full resroration by dam removal could lead to several problems. Depending on how it was managed during dam removal, sedi- ment flushed from the drained Lake Powell mighr overwhelm the river- ine environment of rhe Grand Can- yon, possibly destroying some post- dam riverine resources, such as riparian marshes, and potentially No'" Mod.era~; fluctuations affect fi.sh stranding in uuwarer and campsire stability Muunum power revenues; rapid, erratic,.aseasonal dam releases; flood control with occa- sional unplanned relea~s; minimal protection of eco- ~ystem resource~ Maxuni=! Nolle Low: v~geu.tlOn invasion of some campsires Maximiz~ biodi- versity; maximize biological produc. riviry; maximize reaeational oppor- tunities;conltrain maximum and minimum releases SmaJito moderate production Load-following is restricted; base loading is IDcreased Simulared natural Simul1te some Ustexisting lncre.ased endan- Seasonally Load_following Minor sea.sonal Low: reduced sbade due ecosysrem pre-dam ecological structures to gered fish habitllt; varying or bast load, COlUtr.aints to vegetation loss at processes .and par- incre.ase pre-dam mcre.ased growth production depending on some camps; potentia.! tially restore some resources of upper riplUian season effect on tailwuu prt-dam re!.Ources ?one ~ege'Carioni fi~heC}' larger sand bars; less-difficult rapids Substantially Extensive restora. Modifystruo:- Substantially restore Seasonally Load-following Seasonal High: potentially reduce restored tion of pre-cLJm tures: sediment pre-dam hydrology varying or bast' load, constraints taiJwaterfisbery; ecosystem processes and bypass and/or and sediment trans- production depending on change characterUtics management thermal pOrt; restate aIU\Ua\ season of white-water boating elements modification range of water [emp- In some seasons erature.i; restore pre- dam lands~pe; restore ~ndangered fish habitat Fully rescored Anempt complete Remove dams; Restore pre--clam Small or no Smalle(power Elim.inareflexi- High: e1iminilre tall- ecosystem resroration of pre- remove non. hydrology .and power pro- production bilityin wllter water fishery; change dam processes native fish and sedunent transport; ducrion traosfers ch.aracteristicsofwhitc. and resources vegetarion only nao...e fishes water boating in some and vegetarion OCCllI """'"' tion and on rhe seasonal flexibility of water transfers between the upper and lower basin. . Full restoration of the river is an ambiguous management goal that has not been described precisely and may not be possible. We define this goal as restoration of all pre-dam ecosystem resources and processes by removal of flow regulation. Sev- eral differenr pre-dam standards might be considered as a goal. Resto- ration of a wide range of hydrologic variability might be accomplished by removing Glen Canyon Dam, but the full range of varia bility could not be restored unless all upstream dams and diversions were also removed. Even with this substantial efforr, the river environment could not be re- turned to its 19th-century condition because many alien species, such as saltcedar, non-native fish, and non- September 1998 rhreatening some pre-dam resources. Moreover, the hydroelectric power produced by Glen Canyon Dam would have to be generated else- where or matched by energy conser- vation. In addition, mandated water transfers between upper- and lower- basin states would require grearer annual fluctuations in the volume of water stored in Lake Mead. Table 4 shows the expected ef- fects of some of the engineering tech- niques that could be used to imple- menr the different management goals. Some techniques have also been ana- lyzed by the US Deparrment of Inte- rior (USDI 1995). In some cases, our predictions differ from those conclu- sions, either because additional in- formation has become available or because our interpretations of spe- cific research findings differ. Assess- 743 ;"1 iI' ;:1 ~. if' '.. :[ '. , .:.' ~ ".. . ~'.". '~I ~t~; : ;;4 ~:4~ , ~",- " b'. L...... ~ '.' ". .. :~T-' .. .... (: :~::.: ~t4S ~;;~l'J ..1;:.1;; :....,.,Jo .'