Impacts of hydrologic and geomorphic alteration to the availability of
shallow, low-velocity habitats in an intensively managed arid-land river
Abstract
This study seeks better understanding of linkages between channel
morphology, streamflow, and aquatic habitat for the effective
rehabilitation of imperiled species in rivers subjected to intensive
water resource management. We focused on the variability of shallow,
low-velocity (SLV) habitats over 50 years for a 56 km reach of the Rio
Grande of central New Mexico (Middle Rio Grande). Hydraulic models used
topographic data obtained through long-term systematic monitoring
between 1962 and 2012 to derive relationships between discharge and SLV
habitat availability. We developed a temporally integrated habitat
metric (TIHM) to facilitate quantitative comparisons of SLV habitat
availability over seasonal hydrologic periods (base flow, spring runoff,
and summer low flow) for selected years representative of contemporary
discharge variations. Results showed that SLV habitat availability, as
captured by TIHM values, decreased on average by 83% over the study
period (1962–2012), corresponding to completion of Cochiti Dam (1973),
which profoundly altered flow and sediment regimes. Resulting channel
incision and floodplain disconnection, caused shifts in
discharge-habitat relationships whereby considerably higher discharges
are required to produce equivalent increases in SLV habitat availability
relative to pre-dam conditions. Ecological implications of losses to SLV
habitat availability include recovery of the federally endangered Rio
Grande Silvery Minnow Hybognathus amarus.