Engineered channel controls limiting spawning habitat rehabilitation success on regulated gravel-bed rivers

Abstract

24In efforts to rehabilitate regulated rivers for ecological benefits, the flow regime has been one of 25 the primary focal points of management strategies. However, channel engineering can impact 26 channel geometry such that hydraulic and geomorphic responses to flow reregulation do not 27 yield the sought for benefits. To illustrate and assess the impacts of structural channel controls 28 and flow reregulation on channel processes and fish habitat quality in multiple life stages, a 29 highly detailed digital elevation model was collected and analyzed for a river reach right below a 30 dam using a suite of hydrologic, hydraulic, geomorphic, and ecological methods.

Backwater control on riffle–pool hydraulics, fish habitat quality, and sediment transport regime in gravel-bed rivers

“…10 Second, recognizing that in a straight confined reach lateral and longitudinal variation in 11 U in a river is highest at low Q (Clifford and French, 1998), detailed model validation of H and 12 U on the Trinity River was performed at 12.9 m 3 s -1 . Predictions at two of the five cross-sections 13 evaluated in detail by Brown and Pasternack (2007) show the typical results, with H accurately 14 predicted and U predicted less well (Fig. 3).…”

“…21 The second pool-riffle-pool configuration consisted of a slender, steep diagonal bar ( was distributed across the channel in proportion to the cross-sectional area of each boundary 9 mesh element. These assumptions were validated by measuring H and U near the upstream 10 boundary in the reference reach (Brown and Pasternack, 2007). WSEs at the downstream end of 11 the reference reach were measured at Q's between 8.5-170 m 3 s -1 using a total station to obtain a 12 stage-discharge rating curve useful for simulating any flow in this range.…”

“…Acceptance of the numerical 4 approach requires reasonable confidence in the predictive utility of FESWMS for the conditions 5 explored in the study. As reported by Brown and Pasternack (2007), three different tests 6 assessed model uncertainty for the Trinity River reference reach. First, the range of E values in 7 model output was checked against field-based estimates calculated using the same equations with 8 H and U measurements and taken in the real reach at the spawning discharge.…”

“…Riffles and pools are a well-researched topic in fluvial geomorphology 22 (Gilbert, 1914;Keller, 1971;Richards, 1976;Clifford and Richards, 1992; Sear, 1996; 23 Thompson et al, 1999) and aquatic ecology (Gorman and Karr, 1978;Brown and Brown, 1984; 1 Giller and Malmqvist, 1998). Partly due to numerical modeling studies it is now understood that 2 "self-maintenance" of the relief between riffle crests and pool troughs through time depends on 3 two scales of channel non-uniformity that induce flow convergence routing (Carling, 1991 when discharge is less than bankfull, longitudinal variations in channel shape drive flow 6 convergence over riffles causing gradual incision, armoring, and a decrease in riffle-pool relief 7 (Brown and Pasternack, 2007). During infrequent overbank floods, lateral variations in channel 8 and valley shape drive flow convergence over pools causing them to scour and thereby restoring 9 riffle-pool relief.…”

Reach Scale Application of Uav+sfm Method in Shallow Rivers Hyperspatial Bathymetry

“…Nowadays, many rivers across the world are highly regulated and changed either in flow or sediment regimes (Brown and Pasternack, 2008). Rehabilitation of these rivers is an increasing demand and needs sophisticated tools to assess the current condition of the river.…”