WSP12518 - Laserfiche WebLink

Home Browse Search

21 base flows has allowed for re-establishment of riparian vegetation as well as redevelop- has become fra.gmented. Analogously, prairie restorationists are finding that it is not ment of aquatic micro-habitat features such as pools and runs (Hill & Platts, 1998). In always appropnate to rest~re ~atural ~e ~egimes to tiny patches of prairie, because the Utah, the U.S. Bureau of Reclamation, through the Utah Reclamation Mitigation and net effect can be ~ re?uct1O~ m species diversity (Collins et aI., 1998). Conservation Commission (URMCC), is restoring a portion of the Provo River, as ~n~1:?er. co~phc~non ans~s ~ecause .of the high. degree of temporal hydrologic mitigation for riparian degradation resulting from Federal reclamation projects. The van~bility In and regtons. Which ume-penod defines historic norms? How much can we Provo River Restoration Project seeks to modify the geomorphology and hydrology of de~ate from these norms ~efore we alter biotic components in unacceptable ways the river to create a more naturally functioning riparian system. The project operates (Richter et al., 1997 b)? Will ecosystems be sufficiendy restored if we allow for the according to an 'ecosystem restoration standard' that integrates multiple aspects of the 25-year return ~ood but not the 100-year return flood? What if we increase flood environment (URMCC, 1997). Unfortunately, full restoration of water and sediment frequency to twice per year rather than three times per year? Which flow regime flow is prevented by a new, upstream dam. components are most ecologically sensitive or influential? A small deviation in ground Another case in point is the Truckee River in Nevada. The U.S. Fish and Wildlife wat~r .de~ths or flood timing may cause greater change than, for example, a small Service began managing Stampede Reservoir along the Truckee River for occasional devlanon !n flood I?agnitude. What are the consequences of restoring flood waters but spring flood release, to stimulate spawning of endangered fish species including the not assocl~ted sediments? Such questions demand research. In restoration contexts cui-ui (Chasmistes cujus). An ancillary benefit was establishment of Populus jremontii these ques~ons could be tested using an adaptive management approach until uncertain~ seedlings, which also depend upon appropriately timed floods. Gourley (1998) states, 'A levels decline. whole array of ecosystem components may begin to recover w1).en restoring a basic , ~ere is a compelling reason to study the relationships between stream flows and ecosystem process', such as. the natural flow regime of a river. The chances of meeting npa!lan. ec~system s~cture and function: competing pressures on water resources. the needs of many native species and providing sustainable ecosystem improvement are While npa~an restoranon efforts are on the increase, so too are water development increased if we take an ecosystem approach that restores hydrologic and geomorphic an~ extracnon pressures on streams and aquifers. We are in the midst of a water crisis processes, including flood disturbance (Bayley, 1991; Stanford et al., 1996). However, regtonally.and globally (Dud~ & EI-Ashry, 2000). Although per capita municipal wate; the Truckee River ecosystem and many others remain under threat due to continued consu~pnon has decreased m the United States, overall human population size is up demands on stream water, barriers imposed by dams, and lack of restoration of the full and so IS .total wat~r u~e. Desert.cities, including Las Vegas and Phoenix, are among the complexity of the flood regime. most ~pldly growmg m the Uruted States, putting increasing pressure on limited water Approaches that are less self-sustaining and more contingent on human intervention supplies, ~eople even argue over the rights to water run-off from irrigated lawns continue to be undertaken. For example, a $90 million effort is underway to restore (Oad & DISPI~O, 1997). Irrigated agriculture continues to use the largest share of the Sonoran riparian vegetation to a dewatered section of Phoenix's Salt River. The Rio I ~ater resources m th.e south-western United States, with most going for production of Salado project is a joint effort by the City of Phoenix, U.S. Army Corps of lli,:est~ck ~eed: ElectI?cal power grids are at their limit, a consequence in part of years of Engineers, and other groups, and is funded largely by Federal monies. Goals include ! reJecnng mvesunent In solar and other renewable power sources; thus, pressures are high creation of wildlife habitat and passive recreational opportunities: indirect benefits I ~o manage streams for hydro-power production. Where there is competition for a lim- including economic revitalization of ne~ghborhoods a~ong the river corridor al~o a~e " It~d resource, such as water, one must be able to justify the ecological importance of anticipated. While the outcome of thiS effort remaInS to be seen, the project IS vutUally every drop. conceptually flawed as a trUe ecosystem restoration effort because i~ involves I Resear~h into env,ironmental ~ater needs int~nsi~ed in the 1970s and 1980s, triggered artificial approaches that do not address the root causes of ecosystem degradanon. There 1 by fish~nes ecolOgiSts who Wished to quannfy m-stream flow needs for declining are no plans to release water or sediment from upstream dams or to recharge the alluvial 1 populanons of fish (Maddock, 1999). Ecologists soon realized that in addition to aquifer. Rather, the plan calls for releasing pumped ground water into e~~av~ted surface l, m-channel flow nee?s, ~ere wa.s a ~eed for over-bank flows and sub-surface (ground- channels and planting 75,000 contract-grown trees. The rehabilitanon efforts l water) flow.s to mamtam the npanan vegetation that helps to shape aquatic habitat probably will result in creation of an urban park with some wildlife habitat value. It i featur~s (Hill et al., 1 ?91). Stu~es to determine the water needs of riparian vegetation remains to be seen how biodiversity, bioproductivity, and ecosystem resilience will! have SInce branched In many dIrections. compare to that of free-flowing streams, in the absence of a restored flood regime and ~ One branch ~ncludes transpiration studies, which seek to determine how much water ground water source, and without connectivity to high-quality riparian ecosystems. j a plant populanon or a~semblage needs by asking how much it uses. Techniques ranging ; from canopy-scale ffilcrometeorological measurements of heat flux to plant-scale i measurements of sap flow and heat-pulse velocity, have revealed a wide range of Natural stream flow regimes : resp~n~~s to the. qu~stion of 'how.much water does a patch of riparian vegetation 'i reqwre. . Tran~p1T8non rates vary With stand composition, biomass strUcture, and plant As a broad restoration guide, restoration of natural stream flow regimes is fundamental; age. Along Arizona's San Pedro River, transpiration rates among Populus jremontii (Poff et al., 1997). The natural flow regime hypothesis states that riverine. species i, pa~ches ranged from. 3 to 6 rom per day (Schaeffer et al., 2000). Young, densely- require the temporal and spatial pattern of stream flow to which they h~ve ad~pted over) foliated st~~ds transplr~d more water than did older stands, although individually, old time. Thus, to maintain native riparian ecosystems, one must retam regIOnal flow.; P.. fremontu tre~s o:a~splred ~ore water than young ones. Transpiration rates also vary regimes. However, the specifics of implementation are complicated byma ny factors. For 1 With ",:ater a~ailability (DeVitt et al., 1997). Populus trees along the San Pedro River one, the context within which natural flows exert influence has changed. Because so k transplr~d twice as much water ~hen growing at sites with shallow vs. deep ground water many factors that influence riparian strUcture and function have been altered, full ~ (Goodnch et al;, 2000). Flood-mundated Tamarix ramosissima along New Mexico's Rio restoration of natural flows may not be the preferred option in all circumstances. For 1 Grande transpI~ed twice ~s. much water as did those that were not flooded (Cleverly example, very large scouring floods may not be desirable if a stream reach has become l ~t al., .2000). BI~produ~nVlty and transpiration rates of other riparian plant species, detached from potential post-flood recolonization sources, as might occur if the habitat 1 mcludmg Prosopzs veluuna and Sporobolus wrightii, vary depending on the quantity of RESTORATION OF RIPARIAN VEGETATION OF FLOW REGIME 20 J. C, STROMBERG c::.:' <.::) c.,..:) 1.',--. r;.:.') ~-~