Tag Archives: Aidan Doak

Flow variation within the Grand River Watershed: An explanatory exercise

— by Aidan Doak

Hydrologists and environmental scientists often look at river flow through time and focus their attention to the minimum, maximum and average values. These values are used to answer questions regarding dry and wet periods, which can lead to hydrological droughts or floods. Less often do we look at the variation of flow over time, which is an indication of how dynamic or “flashy” a given river location is, and how strongly it may be coupled to rainfall inputs. Flow variability is not only important for characterizing hydrological regimes but also for ecological reasons, as some aquatic species require a variety of flow conditions through their different life stages. With that in mind, I did a quick explanatory analysis of flow records from 22 hydrometric stations across the Grand River Watershed.

Ten years (2008-2018) of daily river flow values were analyzed. The coefficient of variation (CV) of flow, which is simply the standard deviation divided by the arithmetic mean, was computed for individual stations over (1) the whole period of record, (2) for individual years, and (3) for individual months grouped across all years. The goal was simply to visualize whether spatial patterns of flow variability change depending on the year or month considered.

Figure 1 shows, for each hydrometric station, CV values (shown as blue circles) calculated using the ten years of daily river flow data. It clearly shows the larger flow variability of headwater locations, compared to downstream locations.

To accompany the set of yearly maps (Figure 2), I calculated the total annual rainfall using the Laurel Creek rain gauge station located in the center of the watershed (Figure 3). A quick, visual assessment of Figures 2 and 3 shows that on a yearly basis, CV values do not increase or decrease monotonically as we move from the headwaters downstream. Also, CV values are not necessarily higher or lower in years with less rainfall.

Seasonality of flow variation is evident when the data is displayed monthly (Figure 4), but this time again the location with the highest variability are located in the headwaters. While those results are not surprising, they do highlight the critical importance of headwaters for the hydrological and ecological integrity of watersheds.


URA fieldwork project: nutrient concentrations in select rivers and wetlands in Guelph, ON

— by Aidan Doak, on behalf of myself and Thanuja Thavarasa

On May 8th, 2019, Thanuja and I kicked off our summer undergraduate research assistant (URA) positions at the University of Guelph. There were many potential projects planned for the months to come and a water chemistry analysis project was at the top of our list. The goal was to observe and compare any relationships between nitrate and phosphate concentrations in different water systems within the Grand River Watershed. The city of Guelph, located right in our backyard, became our primary focus. We collected water samples from six sites after significant rainfall events.  We have provided a map showing our six site locations below (Figure 1) and a table displaying sampling dates and precipitation totals since the previous outing (Table 1).

Samples were tested for electrical conductivity and oxygen reduction potential in the field. Afterwards, they were brought back to the lab for turbidity measurements, filtration and analysis of nitrate and phosphate concentrations. We have compiled our data and graphed some of our results below. The straight blue line in each figure highlights the 0.03 mg/L provincial water quality standard for phosphate.

The Eramosa River and the Speed River were our two river sites, with relatively wide channels (Figure 2A and 2B). Both sites demonstrate a similar nutrient behavior; consistently higher concentrations of nitrates compared to the wetland sites (Figure 3), and phosphate concentrations that vary over time more compared to wetland sites. Phosphate concentrations fluctuate within 0.03 mg/L of the provincial water quality standard. The known, higher mobility of nitrate compared to phosphate could explain this behavior. The high levels of nitrate are potentially a product of recent rainfall events, washing nitrates downstream.

A riparian wetland located next to the Speed River was sampled at two locations; the first was closest to the river and the second was adjacent to a walking trail (Figure 3A and 3B). The wetland experienced many expansions and contractions throughout the two-month sampling period. On May 21st, there was no surface water at the Speed River Wetland Trail location so we could not take a sample. The Speed River Wetland Trail location experienced phosphate concentrations three times larger than the provincial standard, while the adjacent Speed River Wetland location had a phosphate concentration that was ten-fold the same standard. The ability of soils to retain phosphate, paired with the expansion and contraction characteristics of the wetland adjacent to the Speed River, may explain those dynamics. Wetlands are nutrient sinks as they prevent nutrients from reaching rivers and streams, which is an environmental benefit.

The Solstice Wetland (Figure 3D) exhibited a different relationship between phosphate and nitrate concentrations compared to the other river and wetland sites. The Solstice Wetland behaved as a perennial wetland as it always had surface water in the depression during the two-month sampling period. On the other hand, the Speed River Wetland is intermittent: it expanded and contracted to the extent that no surface water was present on multiple sampling days. At the Solstice Wetland site, nitrate and phosphate concentrations were strongly correlated, as indicted by their synchronous increasing and decreasing behaviors.



If you were wondering why the Dairy Bush was blue… It was us.

— by Thanuja Thavarasa, on behalf of myself, Aidan Doak and Jamie Bain

Water flow through soil is quite complex. It can move either vertically or horizontally dependent on a variety of factors like soil texture and different types of rainfall events. It can be valuable to know these water flow patterns since they can be used, for instance, to track and regulate the movement of harmful nutrients (like phosphate) to rivers and lakes.

Here is a quick video that shows our work in the field from our own perspective.

At the University of Guelph, the Dairy Bush is divided into two adjacent sectors: a forested area and a grassland area. After scouting the location, we thought it would be interesting to compare and contrast water flow patterns between these two land covers. Thus, on June 3rd, 2019, Genevieve, Aidan, Jamie and I set out to prepare two 1 m by 1 m plots. The idea behind this project was to evenly spread 30 L of water across the plot. The water was dyed with an environmentally friendly blue dye prior to the experiment. After a couple of days, the goal was to excavate these plots and visualize soil water flow patterns via the blue soil stains left behind by the blue water. We ran into a water application problem on the grassland plot due to tall shoots and strong winds. Fortunately, we were still able to successfully saturate the plot with the 30 L of water.