Numerical modelling of climate change impacts on Saint‐Lawrence River tributaries

Abstract

The impacts of climate-induced changes in discharge and base level in three tributaries of the Saint-Lawrence River, Québec, Canada, are modelled for the period 2010-2099 using a one-dimensional morphodynamic model. Changes in channel stability and bed-material delivery to the Saint-Lawrence River over this period are simulated for all combinations of seven tributary hydrological regimes (present-day and those predicted using three global climate models and two greenhouse gas emission scenarios) and three scenarios of how the base level provided by the Saint-Lawrence River will alter (no change, gradual fall, step fall). Even with no change in base level the projected discharge scenarios lead to an increase in average bed material delivery for most combinations of river and global climate model, although the magnitude of simulated change depends on the choice of global climate model and the trend over time seems related to whether the river is currently aggrading, degrading or in equilibrium. The choice of greenhouse gas emission scenario makes much less difference than the choice of global climate model. As expected, a fall in base level leads to degradation in the rivers currently aggrading or in equilibrium, and amplifi es the effects of climate change on sediment delivery to the Saint-Lawrence River. These differences highlight the importance of investigating several rivers using several climate models in order to determine trends in climate change impacts.

Using the UKCP09 probabilistic scenarios to model the amplified impact of climate change on drainage basin sediment yield

“…Figure 4 also highlights the increase in the highest sediment yields, in particular for the 2070-2099 High emissions scenario (totals greater than 5 000 000 m 3 ). Such increases in sediment associated with climatic increases in rainfall are broadly in line with soil erosion studies (Favis-Mortlock and Guerra, 1999;Chaplot, 2007) and channel models (Verhaar et al, 2010). (Holm, 1979 ) is shown in white in the left hand panel; the variability in these simulations comes from stochastic variability alone.…”

“…Channel and upstream sediment inputs are considered, but hillslopes are not explicitly modelled (and linked) as with landscape evolution models. Verhaar et al (2010) modelled future changes in the Saint-Lawrence River, Quebec, using a one dimensional hydraulic model. Seven scenarios of future discharges under different climate change conditions were simulated and all led to increases in sediment delivery.…”

Prospects and challenges of simulating river channel response to future climate change

“…However, flood risk can also partly be compensated for by bed incision during more frequent extreme events (Verhaar et al, 2011). Increasing average bed material and suspended sediment delivery have also been predicted for the St. Lawrence River (Table 1: Verhaar et al, 2010Verhaar et al, , 2011. Even without change to base level, increases in average bed material delivery are expected according to these studies, although the magnitude of simulated changes depended on the choice of GCM and the trend over time related to whether the river is currently aggrading, degrading or in equilibrium (Verhaar et al, , 2011.…”

“…Even without change to base level, increases in average bed material delivery are expected according to these studies, although the magnitude of simulated changes depended on the choice of GCM and the trend over time related to whether the river is currently aggrading, degrading or in equilibrium (Verhaar et al, , 2011. Verhaar et al (2010) showed that a fall in base level leads to degradation and increased sediment delivery in river channels that are currently either aggrading or in equilibrium, amplifying the effects of climate change on sediment delivery. Of particular interest is the finding that the magnitude of base level fall is more important for future channel development than its duration, that is, whether the fall was sudden or more prolonged.…”

Effect of climate change on navigation channel dredging of the Parana River

“…Sung et al (2006), De Wit et al (2007 and Millerd (2011) focused on water-level modification due to variations in hydrology that would eventually impact navigation. Bed-level change effects on navigation channels were considered to a lesser extent by Verhaar et al (2010).…”