Channel adjustments of the lower Trinity River, Texas, downstream of Livingston Dam

Abstract

Channel cross-sectional changes since construction of Livingston Dam and Lake Livingston in 1968 were studied in the lower Trinity River, Texas, to test theoretical models of channel adjustment, and to determine controls on the spatial extent of channel response. High and average flows were not significantly modified by the dam, but sediment transport is greatly reduced. The study is treated as an opportunistic experiment to examine the effects of a reduction in sediment supply when discharge regime is unchanged. Channel scour is evident for about 60 km downstream, and the general phenomena of incision, widening, coarsening of channel sediment and a decrease in channel slope are successfully predicted, in a qualitative sense, by standard models of channel response. However, there is no consistent channel response within this reach, as various qualitatively different combinations of increases, decreases or no change in width, depth, slope and roughness occur. These multiple modes of adjustment are predicted by the unstable hydraulic geometry model. Between about 60 km and the Trinity delta 175 km downstream of the dam, no morphological response to the dam is observed. Rather than a diminution of the dam's effects on fluvial processes, this is due to a fundamental change in controls of the fluvial system. The downstream end of the scour zone corresponds to the upstream extent of channel response to Holocene sea level rise. Beyond 60 km downstream, the Trinity River is characterized by extensive sediment storage and reduced conveyance capacity, so that even after dam construction sediment supply still exceeds transport capacity. The channel bed of much of this reach is near or below sea level, so that sea level rise and backwater effects from the estuary are more important controls on the fluvial system than upstream inputs.

Channel Planform Dynamics Monitoring and Channel Stability Assessment in Two Sediment-Rich Rivers in Taiwan

“…This finding indicates that valley width plays a key role in braided degree, active channel width, and channel activity. In terms of braid index, as long as the background environment has abundant sediment (mainly gravels and sands in this case), steep valley slope, and frequent flood events, the wider valley could provide more space for developing braided channels [23,24] and also main channel shifting [25]. The highest braid index occurs in Z7 in the Zhuoshui River and G3 in the Gaoping River.…”

Channel adjustments in response to the operation of large dams: The upper reach of the lower Yellow River

“…A number of studies deal with the complex response of alluvial river channels due to dam construction (Xu, 1990;Sherrard and Erskine, 1991;Phillips et al, 2005). There are, however, few investigations on alluvial sand-bed rivers with very variable flow regimes and suspended sediment loads which are comparable to the Yellow River (Chien, 1985;Xu, 2001;Hu et al, 2006) (Tables 1 and 2 The exponents b and β show a decreasing trend but f and m an increasing trend.…”

“…Petts (1979) suggested that such adjustments vary spatially and change with time in response to the alteration of flow regime, and Xu (1990) presented further detailed discussion on the complexity of downstream temporal responses using evidence from laboratory experiments and field investigations. Phillips et al (2005) found multiple combinations of increase, decrease or no change in width, depth, slope and roughness in response to dam regulation. Although there have been attempts to generalize the hydrogeomorphic effects of impoundment (Brandt, 2000a,b;Petts and Gurnell, 2005), it remains difficult to predict channel adjustment downstream of dams because of differences in dam operation modes since their construction.…”

“…However, the downstream changes of flow and sediment regime caused by dams can vary significantly between river reaches and over time. The influence of dams on flow and sediment regime and subsequent channel morphology has long been a concern of fluvial geomorphologists and hydraulic engineers (Arroyo, 1925;Malhotra, 1951;Gregory and Park, 1974;Petts, 1979Petts, , 1980Graf, 1980Graf, , 1999Graf, , 2006Williams and Wolman, 1984;Chien, 1985;Andrews, 1986;Gregory, 1987;Carling, 1988;Xu, 1990;Phillips, 2003, Magilligan andNislow, 2005;Petts and Gurnell, 2005;Phillips et al, 2005;Pan et al, 2006;Singer, 2007;Magilligan et al 2008;Zahar et al, 2008;Chen et al, 2010;Fu et al, 2010).…”

“…The above range of studies has demonstrated that the stream channel downstream from a dam can exhibit an interactive combination of adjustments, referred to as complex responses (Petts, 1979;Xu, 1990;Sherrard and Erskine, 1991;Benn and Erskine, 1994;Phillips et al, 2005). Petts (1979) suggested that such adjustments vary spatially and change with time in response to the alteration of flow regime, and Xu (1990) presented further detailed discussion on the complexity of downstream temporal responses using evidence from laboratory experiments and field investigations.…”