WSP07211 - Laserfiche WebLink

Home Browse Search

1583 Maintaining srable water levels from mid August ro November lends stability ro the reservoir, fut- rhet enhancing productivity. 2. Water Preferences For Riparian Habitats a. Arkansas River Riparian and wetland resources in the srudy reach are largely modified. A century of road and rail- way consrrucrion, dams, irrigarion developmenr. conversion of/and to agricultute, residential development, and othet modifications have influ- enced the riparian resources present today. Modifications are genetally centered around: . Vegetation manipulation -: land use activities such as recreation and grazing, introduction and invasion of exotic vegetation, selective har- vesting of certain riparian species. etc. . Watershed alter:uion - land use activities such as roads, logging, agriculrure. mining. and urbanization that affect facrors such as inftlrra- tion, runoff, sediment supply, and water quality. . Direct modification -- channelization. drain. ing, filling, conversion to other uses, ere. . Hydrology alteration - water diversions. water imporrarions, storage, etc. Capability and potential of most tiparian and wetland resources within me study area is deter- mined a gteat deal by the natural shape and form of the tivet corridor that is cteated by geology of the area. Much of rhe Arkansas River is bounded by rock, is narrow, and confined due ro the deep canyon landform. Many reaches which were con- fined narurally are now even more confined because of railway and highway construction. The canyon serring, coupled with high flows, limits soil development and plant rooting abilities. However, some reaches are less confined, and have meander bars and streamside margins with a limited band of riparian vegetarion. Downstream of Canon City, and the shorr reach between Leadville and Granite, have well-developed flood- plains wirh substantial riparian and werland vege- tation. The majority of rhe riparian and werland vegetation is composed of grasses-sedge-rush, wil- lows (several species), alders, bitch, and COtron- wood. Rarher rhan quantifYing the exact changes ro be expeered from flow alterations, the focus of this water needs assessment was co review the litera. rure related (Q riparian communities and identify general rdationships and effects that river man- agers should keep in mind while managing flows. Determining the exact impact of either or large or small scale flow alterations on Arkansas River riparian communities would require an exhaus- rive, long-term study rhat is bevond rhe scope of the present Water Needs r\.ssessmenr. The unique serring of each riparian area along rhe river. in terms of geomorphology. groundw~l[er levels, and gainingllosing stream teaches. also makes it difficult ro predict the effects of flow modification without intensive local study. For example, in rhe Brown's Canvon reach. each lOO cfs increase in Hows increases me Water surface elevation by 3% ro 5%, while in rhe Floodplain sjre, the jncreased water surface elevation is less because of the broader channel. However, the impact from a 100 cfs increase in flows on vegeta- rian will be greater in the Floodplain site, because rhe vegetation line at Floodplain is closer in eleva- tion co me mean annual water surface elevJ.cion. There are rhree facrors which are rhe most critical in maintenance of riparian habitats: (I) maintain- ing rhe hisrotic ftequency and duration of floods, (2) maintaining growing se:l.Son groundwater lev- els in areas adjacent to the srream, and (3) main- taining the annual and seasonal variation in the hydtograph. The riparian community is a product of the long- term hydrolog:.' of rhe river. so fairly large vatia- rions in flow for one year will likely not have a significant effeer. Consistently higher or lower flows, however. willlikelv alter rhe extent and location of riparian vegeracion. The outcome of Row manipulation is more likely ro be the evolu- cion of:J. new riparian J.rea which is a different widrh and elevacion, rather rhan elimination, enhancement, or large changes in rhe ovetall acreage of the riparian community. 31