TECHNICAL REPORTS

Pilot water quality report for streams discharging into W̱E¸NÁ¸NEĆ/Hwune’nuts (Fulford Harbour)
P.S. Ross, J.A. Millson, A. Parkinson, and S. Scott, 2023

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In brief
[…] We conducted a small-scale study of water quality in seven creeks entering Fulford Harbour at three points in time in 2022 and 2023. Measurements were made of basic water properties in situ, including temperature, conductivity, pH, dissolved oxygen (DO), and flow. […]

Basic freshwater properties data fell within the range measured previously both in Fulford Harbour streams and at other freshwater sampling sites on Salt Spring Island. […] There were no exceedances of BC Environmental Quality Guidelines for the protection of aquatic life for any of the water properties or metals. Fecal coliforms were detected in 93% of water samples, and E. coli was detected in 91% of samples, indicative of land-based biological contamination of creeks from wildlife, livestock, pets and/or humans. Fecal coliform [and E. coli counts] were highest in summer […]. Variations in E. coli in some creeks highlight the potential for sporadic releases of pathogens into Fulford Harbour. […] [This is concerning given the] anticipated future re-opening of shellfish harvesting […]

Water diversion license limits for St. Mary Lake
Donald Hodgins, 2018

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In brief
The Province issues licenses for surface water withdrawal [that specify] the maximum amount that can be withdrawn over a defined period of time, usually one day or one year. For St. Mary Lake, all licenses total 573 dam³ [1 dam³ = 1,000,000 L] for the critical June-October summer season. However, for an extreme drought the available safe yield during summer is about 350 to 380 dam³, substantially less than allowed by license. […]

[T]he basic design principle is to allocate water licenses up to a limit that is available for climate average hydrological conditions, taking critical environmental flow thresholds into account. The Province recognizes that the full allocation will not be met during droughts, and has implemented a complex procedure for restricting or denying withdrawals. […] The weaknesses [of this principle] are obvious: there are dry winters when the runoff is inadequate to replenish the fully allocated storage, and there are summer droughts that result in significant shortages of water to meet the licensed withdrawal total. Periods when restrictions come into force are inevitable.

Current demand appears to be well below the licensed total for St. Mary Lake. […] However, summer demand (June-October) is roughly 340 dam³ without water restrictions, leaving a reserve of about 12% of the safe yield [figure adjusted for environmental flows and evaporation].

Drought-limited water supply and demand for St. Mary Lake and Lake Maxwell
Donald Hodgins, 2018

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In brief
The maximum amount of water available from St. Mary Lake and Lake Maxwell for potable supply is about 1,000 to 1,100 dam³/year [1 dam³ = 1,000,000 L]. This is the limit for the worst drought on record for the past 100 years. It is sufficient to supply about 4,000 single-family dwellings each year. Current demand (2017) is approximately 880 to 900 dam³/yr, leaving a reserve of 15% to 20% of supply (about 170 dam³ or 660 single-family dwellings). Climate change over the next 100 years could potentially reduce this reserve by about one-half. The safe supply reserve would then be less than 100 dam³, or approximately 300 to 350 single-family dwellings. […]

Water diversion licenses issued by the Province for both lakes total 2257 dam³/yr, more than twice the supply available in a severe drought. [This does not] seem appropriate for future planning, and for allocation of the water resource.

Safe yield analysis for surface water resources
Donald Hodgins, 2017

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In brief
[…] There were nine drought years in the total 35-yr record [1981-2005] providing yield estimates that were used for an extreme value analysis. Some key findings are:

• June-October yield values of ~ 415 dam³ [1 dam³ = 1,000,000 L] in 2015 have a return period of about 25 years, with an equivalent annual yield of 705 dam³. 1987, the worst drought year on record, has a return period of 80 years, with a yield of ~ 360 dam³ (annual 612 dam³).

• For return periods of 50 to 100 years, the dry-season yield would be about 380 to 350 dam³ respectively. The annual equivalent is 650 to 595 dam³. Current withdrawals (2014) are about 580 dam³, leaving little additional capacity in St. Mary Lake.

• Increasing the storage until refilling limits withdrawals would provide about 930 dam³ annually, assuming that winter outflows equivalent to what currently is discharged through the fish ladder would be acceptable to the BC Ministry of Environment. If higher environmental flows are required, the benefit of raising the weir is reduced. […]

• The yield calculations for 2009, 2014 and 2015 are considered reliable because of the weir control of outflows and relatively good information on withdrawals. The long-term yield estimates for 1981-2006 are less certain because of possible errors in the discharge estimates to Duck Creek, in withdrawals, and the difficulties is calculating changes in storage from the adjusted water level series. Application of a hydrological model, including a rigorous uncertainty analysis for the yield estimates, should be considered to further support the safe yield assessment.

Linking watershed exports & the ecology of Blackburn & Cusheon Lake, 2014-16
Maggie Squires & Drew Bodaly, 2016

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In brief
Over a 2-year period, a group of volunteer Citizen and Professional scientists closely monitored lake inflows and outflows […] and the water chemistry of tributary streams and lake water […] at Blackburn and Cusheon Lake […]. Chemical measurements included dissolved inorganic and total phosphorus (P), nitrate (NO₃), suspended sediment, and dissolved organic carbon. Calculations included chemical export coefficients for nine tributary and lake inflow and outflow streams, and water budgets and [phosphorus] loads […].

Major new findings include the following:

• groundwater appears to be an underappreciated flow component

• septic field failures at the Cedar View Trailer Park may episodically contribute nutrients to Cusheon Lake

• net dissolved inorganic [phosophorus] load was substantially lower than the previously modeled estimate of [phosphorus] load (CWMP 2007) yet provided realistic predictions of lake water phosphorus concentration

• lake waters undergo strong seasonal cycles including NO₃ depletion-replenishment, and low-high water clarity.

[…] Both lakes were relatively turbid during the winter when flushing with inflow water was frequent, and relatively clear during the spring-summer when inflow and outflow ceased; and, in both lakes, a late summer/early fall algal bloom was triggered by internal mixing (deepening of the epilimnion) and bloom collapse coincided with lake turnover (mixing to the lake bottom). The biomass of algal blooms was greater at Blackburn than at Cusheon.

Lake and bloom enhancement was due, we think, to internal loading via ebullition and flotation of sediment rafts. Based on summer chlorophyll and [total phosphorus] levels in lake water […] Blackburn Lake is between mesotrophy (intermediate productivity) and eutrophy (high productivity) while Cusheon is between oligotrophy (low productivity) and mesotrophy. Both lakes had relatively high mean summer water clarity for their trophic status and likely this was due to zooplankton grazing that kept chlorophyll concentration (algal biomass) lower than expected for late winter/early spring [phosphorus] levels.

Recommendations for improving lake water quality include monitoring outflow from the garbage transfer station (once a garbage dump):

• regular inspection of lakeshore and streamside septic fields (by residents) to detect and repair field failures as soon as they occur

• a halt in activities that discourage beaver dams and log jams at the Cusheon Lake outflow; rewatering of the Blackburn wetlands

• removal of the abandoned pump house and pipes on the Blackburn lakeshore and of the pumps, pipes, and rock dam in the vicinity of the Blackburn Lake outflow

• seeking of public support for the installation of holding tanks where septic fields are within 100 feet of the Cusheon lakeshore.

Nine lakes on Salt Spring Island, BC: size, watershed, inflow, precipitation, runoff and evaporation
John Sprague, 2009

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In brief
SIZE: St. Mary Lake dwarfs all the other lakes of Salt Spring, in size and amount of standing water. St Mary contains about 16 million cubic metres of water, while the other lakes range from a little over 2 million down to only about 0.1 million cubic metres.

INFLOW: [T]he greatest yearly inflows of water occur in Cusheon and Ford Lakes, each with almost 4 million cubic metres per year (m³/yr). […] St. Mary and Blackburn have somewhat smaller yearly inflows of about 3 million m³/yr, followed by Stowell Lake with almost 2 million m³/yr. Inflows to Bullocks, Maxwell, Weston and Roberts Lakes range from 1 million down to less than 0.6 million m³/yr. Diversions into Maxwell Lake have boosted its yearly inflow from last place to sixth place among the nine lakes.

REPLACEMENT TIMES: The fastest are Blackburn and Ford Lakes, which average just over a month [to replace 95% of their water molecules]. Stowell Lake, Cusheon Lake, Roberts Lake, and Bullocks Lakes take about 4 months. Maxwell Lake, after diversion of streams into it, takes almost eight years. St. Mary Lake is the slowest to flush, with a replacement time of almost fifteen years. […]

PRECIPITATION: Yearly rain and snowfall has historically averaged 0.98 metres in the Cusheon drainage basin. The average for all of Salt Spring Island is 0.959 metres in a year.

RUNOFF: The annual surface runoff, directly from the land into creeks, is estimated as 48% [based on a] robust average of eleven estimates by earlier workers at various locations on Salt Spring Island.

[…] Salt Spring lakes are unusual in two respects, compared to “typical” lakes elsewhere in Canada and the world. First, the major inflow of water comes as heavy winter runoff, followed by dry creeks in summer. Second, most of the lakes are of unusual size compared to their drainage basins. Blackburn, Ford and Stowell are small lakes set in relatively large basins. Weston, Maxwell and St. Mary are large lakes in small basins. Roberts, Cusheon, and Bullocks Lakes are more typical in size, relative to their drainage areas.

Phosphorus carried by small culverts into Cusheon Lake
John Sprague, 2007

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In brief
This study assessed seven culverts [under Horel and Cusheon Lake Roads] as a source of phosphorus for Cusheon Lake, and [compared phosphorus concentrations and loads] to those in Blackburn Creek (upstream of Blackburn Lake). […]

The concentration of phosphorus in the culvert water was usually similar to the concentration in Blackburn Creek. However, the first two flushes of runoff had very high concentrations in the culverts — two to three times higher than the creek. Phosphorus apparently accumulated on the land around Cusheon Lake during the dry season, and washed off with the first big rains. Presumably the higher phosphorus is related to human activity in this built-up area. […]

Phosphorus runoff from the upper Cusheon basin
John Sprague, 2007

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In brief
The purpose of this research was to measure how much phosphorus is carried downstream in upper Blackburn Creek during one year. Almost all of this phosphorus is derived from land runoff. The estimate will help to assess the sources of enrichment for downstream Cusheon Lake. […]

[T]he runoff from upstream areas of land was estimated as 0.106 kg of total phosphorus per hectare in one year. This is close to standard estimates for forested land in eastern Canada, and only 19% higher than a value obtained by modelling the land runoff from the Roberts and Blackburn drainage basins.

During most of the year, particulate phosphorus was the dominant form in the water. Dissolved phosphorus, the most readily available form for algae and other biota, was a small fraction of the total. It appeared to have a base concentration of 8 to 24 [parts per billion], probably derived from groundwater emerging as springs. However, during the very first small freshet after the summer dry period, there was a peak of phosphorus which was almost entirely dissolved, not particulate. That peak might largely represent soluble phosphorus from the ashes of “burn piles” and from decay of vegetable matter during the previous dry season. […]

Phosphorus content of certain creeks and lakes in Cusheon Lake basin
John Sprague, 2007

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In brief
In Roberts Lake, on six days when the lake was mixed, the average [phosphorus] concentration was 16.5 [parts per billion]. One measurement in Blackburn Lake, combined with six measurements by the B.C. Ministry of the Environment in 1981, gave an average value of 16.3 [parts per billion] during the season when the lake is mixed.

Roberts Lake is the first in the three-lake system. The creeks feeding this lake drain a small area, and in the early autumn their flows were low. Their concentrations were about 50% of the concentrations prevailing on the same day, further downstream in the system in the lower parts of Blackburn Creek. […] Because the creeks at Roberts Lake are small, their load of phosphorus was only 1% to 8% of the load in Blackburn Creek.

During the winter and early spring, creeks feeding Roberts Lake had surprisingly high concentrations and loads of phosphorus. […]

A hillside that had been clear-cut four years previously, had apparently grown adequate low bushes and ground-cover to control erosion and phosphorus runoff. In springtime samples, the creek draining the clear-cut had water that was clear, with normal phosphorus concentrations of about 10 [parts per billion]. […] Because the creek was small, it contributed a negligible phosphorus load that was only 0.5% of the load carried by Blackburn Creek.

Two streams of runoff water from a new road off Blackburn Road were sampled once by single samples. Total phosphorus concentrations were higher than in Blackburn Creek, the destination of the runoff, but because of their small flows, the phosphorus load was less than a tenth of the load carried by Blackburn Creek. This single small evaluation does not give an adequate assessment of nutrient contributed by the major construction activities for the road.

Hitchcock Creek is a small creek that crosses Blackburn Road, half a kilometre from Blackburn Creek. The flow of Hitchcock Creek averaged 10% of the Blackburn flow for the ten occasions when samples were taken, but the relative flows varied eighteen-fold. The phosphorus concentrations in Hitchcock Creek averaged 72% of those in Blackburn Creek. Because of this lower concentration and much lower average flow, the average load of phosphorus carried by Hitchcock Creek was only 7% of the loads in Blackburn Creek. Both relative concentrations and relative loads were extremely variable.

Along the most downstream section of Blackburn Creek that bordered a modular-home park, a small number of measurements of dissolved phosphorus indicated an average increase of 24 grams of phosphorus per day. That gave some confirmation of an earlier theoretical estimate of a 21-gram increase as the result of normal seepage from septic fields at the modular-home park. […]

Apparant sources of phosphorus affecting Cusheon Lake
John Sprague, 2007

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In brief
[…] The amount of phosphorus [in Cushion Lake] is the overall factor that controls the strength of algal blooms. […] Average phosphorus concentration has been 16.6 μg/L [mesotrophic, = somewhat enriched] in the most recent decade (1996 to 2006).

The deep water of Cusheon Lake is isolated all summer by natural stratification. Decay of algae and other material deoxygenates this deep water, [resulting in] regeneration of slightly more than 25 kg [per year] of phosphorus from the sediment into the bottom water. This recycled nutrient adds on to the yearly external load when lake waters become mixed in the autumn. The load regenerated from the sediment appears to have been increasing over the years, from about 7 kg in 1974-75. This makes it more urgent to reduce the external inputs to the lake. […]

[We estimated phosphorus loads in the three lakes in the Cusheon basin using a “cottage-country” predictive model developed by Drs. Dillon, Rigler and Hutchinson]. The “probable” scenario from the cottage-country model estimated that Cusheon Lake received 92.6 kilograms [of phosphorus] per year from external sources. Adding to that, the internal regeneration of 25 kg from the bottom sediments raises the amount which is mixed into the water to a total of 118 kg. The component sources can be listed as follows:

• 46 kg (39%)
  inflow from upstream lakes, mostly from land runoff in the sub-basins

• 17 kg (15%)
  land runoff in the Cusheon sub-basin

• 25 kg (21%)
  regeneration from the bottom sediment

• 19 kg (16%)
  direct human input from homes around the lake, plus shoreline clearing

• 8 kg (7%)
  direct human input (septic fields) from trailer homes upstream of lake

• 3 kg (2%)
  precipitation and aerial fallout

[…] Having estimated the land runoff of phosphorus to Roberts and Blackburn Lakes, the downstream flow of phosphorus from those lakes to Cusheon Lake was estimated by the model as 46 kg per year. […] The estimated total loading [of phosphorus] can be applied to a widely-known, more general Vollenweider model [which] model predicts a low mesotrophic condition for all three lakes […]. That shows approximate agreement with the current average phosphorus concentrations of 16.3 to 16.6 μg/L in the three lakes.

If the total loading of phosphorus to Cusheon L. were reduced by 18 kg per year (15%), the lake would probably attain an acceptable status in the lower mesotrophic zone. The prediction of 13.5 μg/L of phosphorus as springtime average would be similar to the historic situation before settlement by Europeans [and would meet BC’s upper criterion for protecting fish]. There would probably be fairly satisfactory conditions of minor algal blooms, and few problems with toxic cyanobacteria. This reduction is recommended. […] ([Meeting] the provincial goal for a “drinking-water lake,” would require 38 kg less phosphorus loading to the water [which is an unrealistic objective]).

The recommended reduction of 18 kg of phosphorus could come from any single source, or a combination of sources. The large input from land drainage could be reduced by strict programs of revegetation along riparian areas of all creeks and lakes. Near-elimination of the direct human input from septic fields (25.5 kg) could be done by complete collection of sewage from all residences (or connecting to a specially-built sewer) with central waste treatment. Eliminating regeneration from sediments would also be a solution.

[The] conventional cure of aerating bottom water is not feasible in this shallow lake, and use of a chemical precipitant might not be favoured. […]