Figure 2. Reach profile from
upstream (left) to downstream (right) with representative pool (above
profile) and rock weir (below profile) cross-sections. The asterisk in
the Pool 7 cross-section indicates the stilling welling location.
Vertical exaggeration is 0.08 m.
Over 530 velocity measurements were collected to identify a range of
velocities at each pool feature. Collectively, under all water level
conditions, the cross-section velocity in pool features ranged from
-0.14 m/s to 0.83 m/s. Recirculation zones were located near the channel
banks in 6/11, 7/11, and 10/11 pool features under low, intermediate,
and high-water levels, respectively. Recirculation zones are recognized
as locations where the velocity measurement is a negative value,
indicating flow moving in an upstream direction (Kimura and Hosoda,
1997).
Over 70 velocity measurements were collected in gap and over-weir flow
pathways to identify flow through rock weir structures under different
water level conditions. Velocities in gap pathways ranged from -0.14 m/s
to 1.10 m/s. Additionally, velocities in over-weir pathways ranged from
0.10 m/s to 0.18 m/s. Depending on the water level condition (low,
intermediate, high), the ratio of gap to over-weir flow pathways, and
the total number of flow pathways differs. Under low water level
conditions, there were a greater number of gap flow pathways. As water
level increases to intermediate water level conditions, individual gap
flow pathways merge to form one large gap, and/or over-weir flow
pathways begin to form. Further, as water level increases to high water
level conditions, the number of gap flow pathways minimizes, while flow
over the keystones (over-weir flow) becomes more common. The ratio of
gap to over-weir flow pathways was 17:1, 18:5, and 11:10 under low,
intermediate, and high-water level conditions, respectively.
Swimming characteristics for local fish species within Weslie Creek were
identified. The local fish community was comprised of small-bodied fish
species with specific swim speeds, which were considered in the VRW
design. A comparison between velocity through pool features, rock weirs,
and burst swim speeds (m/s) was completed to identify where fish passage
opportunities exist or do not exist under different water level
conditions. Additionally, the preferred water temperature range for all
local fish species was compared to the measured water temperature
collected at pool 7 to estimate habitat suitability in pool features.
Finally, the vertical distance between weir crest and the downstream
pool at each rock weir was measured to determine if upstream movement is
possible through leaping under both suitable and unsuitable flow
conditions.
Based on fish passability, reach longitudinal connectivity was analyzed
under low, intermediate, and high-water level conditions (Figure 3).
Under low water level conditions (June 22, 2018), 100% fish passability
(passable for all fish species) was achieved through all pool features
and through 9/10 rock weirs (Figure 3 - Low). Under low water level
conditions, there is no gap or over-weir flow through VRW2, which
restricts fish passage (Figure 3 - Low). Under intermediate water level
conditions (June 28, 2018), 100% fish passability was achieved through
all pool features and through 6/10 rock weirs (Figure 3 - Intermediate).
Under intermediate water level conditions, gap and over-weir flow at
VRW2, VRW3, VRW6, and VRW10 exceeded burst swim speeds of one or more
local fish species. However, 1 to 3 pathways were available for faster
swimming species through these weirs (Figure 3 - Intermediate). Under
high water level conditions (July 25, 2018), 100% fish passability was
achieved through all pool features, and through 6/10 rock weirs (Figure
3 - High). Under high water level conditions, gap and over-weir flow at
VRW1, VRW2, VRW3, and VRW9 exceeds burst swim speeds of one or more
local fish species. However, 1 to 2 pathways were available for faster
swimming species through these weirs (Figure 3 - High). It is important
to note that velocity measurements were collected at 60% water depth,
which provides an average velocity for the pathway. Fish are more likely
to pass through the pathway near the channel bed where velocities are
lowest. As such, these velocity values are conservative to inform fish
passage effectiveness. Depending on the water level and rock weir
design, different flow pathways are available for fish passage. At VRW2,
under low water level conditions, the only possible flow pathways were
through orifices. This is true for other low gradient rock weirs (Figure
4a). Further, at a high gradient rock weir (Figure 4b), the vertical
distance between upstream water level and weir crest is minimal, and
therefore connectivity is maintained between upstream and downstream
flows. Figure 4b demonstrates that at a high gradient rock weir, it is
likely that orifice, gap, and over-weir flow pathways are active. An
analysis was conducted to determine if weir gradient at Weslie Creek
influenced fish passability through the reach under different water
level conditions (Table 1).
Table 1. Total fish passability based on rock weir gradient.