In EffetsCumulatifsNavigation/ceanav: Research compendium for project on the assessment cumulative effects of marine vessel activities in the St. Lawrence

Dredging {#dragage}

We thank Simon Blais of Environment and Climate Change Canada and Pierre Michon of the Quebec Ministry of the Environment and the Fight Against Climate Change for the discussions and support.

meta <- read_yaml("../data/data-metadata/int_st_dragage.yml")
show_source(meta$rawData, lang = "en")

The St. Lawrence Seaway has historically been dredged wherever the natural depth would not allow boats to pass safely. Between Montreal and Cap Gribane, which is located downstream from Cap Tourmente, about 30 $km$ from Île d’Orléans, the navigable waterway is approximately 340 km long and artificial banks have added over a distance of about 210 km to ensure safe navigation [@ghd2019]. The waterway has been deepened and widened over time, mainly due to increases in the size of vessels and marine traffic. A historic characterization of capitalization dredging activities -- i.e. dredging to deepen and widen the waterway -- of the St. Lawrence Seaway is described by @cote2007 and @cote2007a. Some portions of the waterway must also be dredged at regular intervals -- i.e. maintenance dredging -- due to the sediment dynamics of the environments. The same is true for certain port facilities along the St. Lawrence and Saguenay rivers, which must ensure the ability of their vessel facilities to operate safely.

In this study, contemporary dredging activities for the period r meta$dataDescription$temporal$start to r meta$dataDescription$temporal$end were characterized. Most of the data on dredged and deposited volumes come from a compilation exercise of dredging activities throughout the St. Lawrence [@mtq2016; @mtq2017; @eccc2020]. Dredging data available in a report assessing the environmental impacts of dredging in the St. Lawrence Seaway completed these data [@ghd2019]. Dredging activities for the Port of Quebec were characterized through discussions with a representative of the Port of Quebec City (Marie-Ève Lemieux, personal communication). Various reports were used to characterize maintenance dredging activities for Port Alfred [@englobe2016; @englobe2017; @melcc2019], and capitalization dredging activities planned for the Port of Montreal at Contrecoeur [@snclavalin2017; @snclavalin2017b; @aeic2021] and for the Port of Trois-Rivières [@stantec2015]. Lastly, data on dredging and disposal sites were transmitted by the Essipit Innu First Nation [@bouchard2022].

The volumes recorded were then plotted for the dredging and disposal sites. Where provided within the reports, coordinates delineating the sites considered were used. Where a single coordinate representing the geometric centre of the sites where dredging would take place was available without additional information on the exact location of the activity, an area with a radius of 100 $m$ was drawn to represent the dredging or disposal area. Where the location was described, or a figure was available in the detailed reports, the dredged and disposal areas were georeferenced manually. The St. Lawrence Seaway dredging and disposal site locations were taken from a database provided by the Canadian Coast Guard [@gcc2021b].

Dredging sites and dredged sediment disposal sites were characterized based on the total volume dredged in $m^3$ during the period considered (Table \@ref(tab:dragageGen)). A total of r length(meta$dataDescription$dragage$volume) dredging sites (Table \@ref(tab:dragageSite)) and r length(meta$dataDescription$depot$volume) disposal sites (Table \@ref(tab:dragageDepot)) were characterized in the study area. It should be noted that the total volumes dredged do not correspond to the total volumes deposited since some of the disposal sites are on land and accordingly, were not included in this study.

Port expansion projects for the Port of Montreal at Contrecoeur [@snclavalin2017; @snclavalin2017b; @aeic2021] and for the Port of Trois-Rivières [@stantec2015] provided plans for capitalization dredging in the coming years. These plans were therefore identified (Table \@ref(tab:dragageGen); Table \@ref(tab:dragagePrevu)).

tab <- as.data.frame(meta$dataDescription$categories) %>%
       select(english, sites, volume, volume_moyen, volume_sd)

tab %>%
  knitr::kable(
    col.names = c("Category", "Number of sites", "Total volumes", "Average total volumes", "Standard deviation"),
    row.names = FALSE,
    caption = "Categories and description of dredging activities recorded in the St. Lawrence and the Saguenay river between 2001 and 2020. The volumes are presented in $m^3$."
  )

tab <- as.data.frame(meta$dataDescription$dragage) %>%
       arrange(municipalite,name)

tab %>%
  knitr::kable(
    col.names = c("Region", "Site name", "Total volumes"),
    row.names = FALSE,
    caption = "Dredging sites and total volumes dredged in $m^3$ in the St. Lawrence and the Saguenay river between 2001 and 2020."
  )

tab <- as.data.frame(meta$dataDescription$depot) %>%
       arrange(municipalite,name)

tab %>%
  knitr::kable(
    col.names = c("Region", "Site name", "Total volumes"),
    row.names = FALSE,
    caption = "Disposal sites and total volumes deposited in $m^3$ in the St. Lawrence and the Saguenay river between 2001 and 2020."
  )

tab <- as.data.frame(meta$dataDescription$dragage_prevu) %>%
       arrange(municipalite,name)

tab %>%
  knitr::kable(
    col.names = c("Region", "Site name", "Total volumes"),
    row.names = FALSE,
    caption = "Capitalization dredging sites and total expected volumes in $m^3$ in the St. Lawrence and the Saguenay river."
  )

The intensity of dredging (Figure \@ref(fig:dragage)), sediment disposal (Figure \@ref(fig:depot)), and planned dredging (Figure \@ref(fig:dragageprevu)) activities was characterized by distributing the total volumes dredged within our 1 $km^2$ grid. For example, imagine a dredging activity that resulted in the extraction of 100 $m^3$ of sediment over a total area of 2 $km^2$ and that this site covers exactly 2 cells of our study grid. This means that the values assigned to the 1 $km^2$ cells would be 50 $m^3$ each.

To do so, we multiplied the total volumes in each $j$ cell of the study grid by the proportion of the area where dredging would take place covering cell $j$:

$$I_{dredging,j} = \sum_{k=1}^{n_j} V_{tot, k} * \frac{A_{j,k}}{A_{tot,k}}$$

where $j$ is a study grid cell, $k$ is a dredging or disposal activity, $V_{tot}$ is the total volume dredged or deposited during the dredging or disposal activity, $A$ is the dredging area where dredging would take place $k$ that intersects a $j$ cell, and $A_{tot}$ is the total area where the $k$ dredging or disposal occurs. This formula calculates an assessment of the dredging intensity in $m^3$. Since we have calculated the intensity in cells of 1 $km^2$, the units of this formula are in $m^3 * km^{-2}$.

knitr::include_graphics("./figures/figures-integrated/dragage-dragage.png")

knitr::include_graphics("./figures/figures-integrated/dragage-depot.png")

knitr::include_graphics("./figures/figures-integrated/dragage-dragage_prevu.png")

EffetsCumulatifsNavigation/ceanav documentation built on April 17, 2023, 1:02 p.m.