RWS Comox Lake Hydrology Final

T e c h n i c a l M e m o r a n d u m

Comox Lake Water Supply Study Phase 1-Hydrology Analysis

Prepared for

Comox Valley Regional District

October 2008

Prepared by

Copyright © 2008 by CH2M HILL Reproduction and distribution in whole or in part beyond the intended scope of the contract without the written consent of CH2M HILL is prohibited.

COMOX LAKE WATER SUPPLY STUDY PHASE 1 – HYDROLOGY ANALYSIS

363908C101_WB102008001VBC i COPYRIGHT 2008 BY CH2M HILL • ALL RIGHTS RESERVED • COMPANY CONFIDENTIAL

Contents

1. Introduction............................................................................................................................ 1 1.1 Conclusions ................................................................................................................ 1 1.2 Recommendations ..................................................................................................... 1

2. Background and Scope of Work ......................................................................................... 2 3. Watershed Characteristics.................................................................................................... 2

3.1 Comox Lake Reservoir.............................................................................................. 2 3.2 Comox Lake Watershed ........................................................................................... 3 3.3 Water Licenses ........................................................................................................... 3

4. Analysis of Water Supply Capacity ................................................................................... 4 4.1 Methodology.............................................................................................................. 4 4.2 Hydrology – UBC Watershed Model ..................................................................... 8 4.3 Hydrometric and Climate Station........................................................................... 8 4.4 Drought Analysis ...................................................................................................... 9 4.5 Water Yield............................................................................................................... 14 4.6 Water Demand......................................................................................................... 16 4.7 Storage Analysis ...................................................................................................... 16

5. References ............................................................................................................................. 19

Exhibits

Exhibit 2-1 Comox Lake Watershed .......................................................................................... 5 Exhibit 2-2 Comox Lake Land Cover......................................................................................... 6 Exhibit 2-3 Current Water Licenses on Comox Lake............................................................... 7 Exhibit 3-1 Browns River and Comox Lake Watersheds’ Characteristics.......................... 11 Exhibit 3-2 Comox Lake Watershed’s Average Annual Water Yield ................................. 13 Exhibit 3-3 Drought Period Modification ............................................................................... 14 Exhibit 3-4 Comox Lake Watershed’s Average Monthly Water Yield ............................... 15 Exhibit 3-5 Comox Lake Reservoir’s Elevation-Storage Relationship ................................ 17 Exhibit 3-6 Average Monthly Water Balance Period, 1999 to 2008 ..................................... 18 Exhibit 3-7 Average Monthly Water Supply Distribution Period, 1999 to 2008................ 19


ii 363908C101_WB102008001VBC

COPYRIGHT 2008 BY CH2M HILL • ALL RIGHTS RESERVED • COMPANY CONFIDENTIAL

Tables

Table 1-1 Comox Lake Watershed Yield.................................................................................1 Table 2-1 Water Licenses on Comox Lake..............................................................................4 Table 3-1 Comparison of Climate Stations .............................................................................8 Table 3-2 Watershed Physiographic Characteristics.............................................................9 Table 3-3 Comox Lake Watershed’s Average Monthly Water Yield................................15

Appendixes

Appendix A UBC Watershed Model and Model Calibration Appendix B Plots of Drought Annual Precipitation and Water Yield

363908C101_WB102008001VBC 1


T E C H N I C A L M E M O R A N D U M

Comox Lake Water Supply Study Phase 1 – Hydrology Analysis PREPARED FOR: Comox Valley Regional District (CVRD)

PREPARED BY: Lawrence Benjamin, Gabor Vasarhelyi, and Jackeline Luque

DATE: October 31, 2008 PROJECT NUMBER: 363908.C1.01

1. Introduction The purpose of this technical memorandum is to report on the Hydrology Analysis for the Comox Lake Water Supply Study – Phase 1. Since this work is highly technical, the conclusions and recommendations resulting from this analysis are presented at the beginning of this technical memorandum.

1.1 Conclusions Based on the information presented in this technical memorandum, it is concluded that:

• The water yield of Comox Lake Watershed is defined in the following table:

TABLE 1-1 Comox Lake Watershed Yield

Condition Yield, m3/s Average 30.31 100-year return period drought year (single year) 16.88 Critical drought period (7 years), which includes a 100-year return frequency 25.82

• Comox Lake has a storage capacity of approximately 94.2 million m3 between its normal maximum and minimum operating elevations of 130.8 m and 135.33 m.

• For a critical drought period between wet years, only 89 percent of the water yield is available for water supply due to the limited storage capacity of the reservoir.

1.2 Recommendations Based on the conclusions of the hydrology study, the CVRD should now proceed with Phase 2 of this study. The following tasks are required in Phase 2:

• Identify potential, future climate change scenarios, and select two extremes (high and low impact) for use in the analysis and that cover the range of potential impacts.

• Estimate the potential impacts of climate change on the water yield.


2 363908C101_WB102008001VBC


• Define the reservoir storage capacity required to maximize the water supply capacity of the watershed for current hydrology, as well as for hydrology impacted by climate change.

• Identify other potential water sources, and determine their supply capacity.

2. Background and Scope of Work In 2005, the CVRD initiated a Watershed Assessment of Comox Lake. The purpose of this work was to identify the major risks to the Comox Lake water source, determine ways to mitigate these risks, and assess water availability.

A key finding of the Watershed Assessment was that the water supply capacity of the Comox Lake Watershed is limited by the available, dynamic storage capacity of the Lake, which is fully licensed for hydro power generation, fisheries habitat support, and domestic water supply.

Currently, Comox Lake is the main water supply source in the region. In light of major infrastructure decisions that will be made in the near future, the objective of this assignment is to review the hydrology of the Comox Lake Watershed and determine its support capacity.

The work will be performed in two phases. Phase 1 is the hydrology analysis, and Phase 2 is the analysis of storage capacity, effect of climate change, and other potential water supplies.

The major work tasks in Phase 1 include the following:

• Define Comox Lake Watershed

• Identify a critical drought period

• Estimate the water yield of the watershed during a 100-yearreturn period drought year using the University of British Columbia Watershed Model (UBCWM)

• Define the water supply capacity of the Comox Lake Watershed with the existing reservoir conditions

3. Watershed Characteristics This section defines the watershed’s contribution to the water supply for various uses, based on the water licenses. The Comox Lake Watershed characteristics are presented in the following subsections. Information in this section is based on the Comox Lake Watershed Assessment – Summary Report (CH2M HILL, 2006).

3.1 Comox Lake Reservoir Comox Lake was developed into a reservoir in 1912 to provide water for the Puntledge Hydroelectric Project. It has the following characteristics:

• The Dam impounds and controls the water level of Comox Lake.

• Water levels on Comox Lake and release of water into the Puntledge River are guided by the Puntledge River Water Use Plan (BC Hydro, 2004). The water use plan balances


363908C101_WB102008001VBC 3 COPYRIGHT 2008 BY CH2M HILL • ALL RIGHTS RESERVED • COMPANY CONFIDENTIAL

water use among varying interests, such as electricity generation, fish habitat, recreation, and municipal water supply.

• The surface area of the Comox Lake Reservoir varies between approximately 1,900 ha and 2,200 ha. The average depth of the lake is approximately 60 m, with the deepest portion being 130 m.

• The operating water level varies between 130.8 m and 135.33 m in summer, which provides approximately 94.2 million m3 of useable water storage within the 4.53-m dynamic operating range of the Lake. Winter operating levels vary between 130.8 m and 134.4 m, permitting approximately 20 million m3 for spring freshet flood storage.

• Comox Dam is a 142-m-long, concrete, gravity structure with a crest elevation of 137.55 m. Outflow is controlled by two sluice gates that measure 4.27 m wide x 7.32 m high. The sill elevation of the sluice gates is 128.93 m. The overflow spillway is 15 m-long at 135.33 m elevation. The Dam is equipped with a fish ladder for fish passage. The probable maximum flood flow is estimated to be 1,500 m3/s, which would result in a maximum lake elevation of 139.9 m.

3.2 Comox Lake Watershed Comox Lake drains a 46,200-ha (462-km2) watershed of mountainous terrain supporting glacial formations year-round. The watershed is largely undeveloped and contains mostly coniferous forests at various stages of maturity. Forestry is the primary industry in the area, and there are several forest roads throughout the basin.

Exhibits 2-1 and 2-2 show the streams that contribute to the Comox Lake Watershed and land cover, respectively. The largest of the streams is the Cruickshank River, which has a contributing area of 21,561 ha and represents 46 percent of the Comox Lake Watershed. The second largest stream, the Upper Puntledge River, has a contributing area of 8,996 ha and represents 20 percent of the Comox Lake watershed.

Two other significant streams, Toma Creek at the south end (2,395 ha) and Perseverance Creek at the east end (2,241 ha), discharge into Comox Lake, with each representing approximately 5 percent of the Comox Lake Watershed. Both Toma Creek and Perseverance Creek are fish-bearing streams. The Perseverance Creek watershed is also the water supply source for the Village of Cumberland. Direct inflows and several smaller streams discharge into the Comox Lake Watershed and contribute 8,893 ha, which represents approximately 19 percent of the watershed.

3.3 Water Licenses Water licenses are typically issued based on the water yield of the watershed during critical drought periods and the reservoir storage capacity that is available to store water from wet periods and will supply water during dry periods of the year. Table 2-1 and Exhibit 2-3 show the current water licenses on Comox Lake (BC Ministry of Environment, 2008).


4 363908C101_WB102008001VBC


TABLE 2-1 Water Licenses on Comox Lake

Current Licenses Licensee Purpose m3/s %

BC Hydro Power generation 28.3 82.54 Fisheries and BC Hydro Fish habitat 5.70 16.62 Comox Strathcona Regional District (CSRD)

Municipal water supply 0.29 0.84

Total 34.29 100

4. Analysis of Water Supply Capacity This section outlines the methodologies for drought analysis and for determining water supply capacity. The hydrologic model and the method used to determine an appropriate climate station are also described. Complete descriptions are included in Appendix A. Following calibration of the model, the Comox Lake Watershed’s water supply capacity was evaluated, along with the existing reservoir storage capacity.

4.1 Methodology The methodology to define Comox Lake Watershed’s water supply capacity involved:

• Delineating the Comox Lake Watershed (Section 3.2)

• Identifying a critical drought period preceded and followed by a wet period

• Estimating the water yield of the watershed during a critical period that includes a 100-year return period drought year using the UBCWM

• Defining the water supply capacity of the Comox Lake Watershed with the existing reservoir

The UBCWM was used to generate water yield for this project. The model uses precipitation and temperature data as input and requires calibration. Appropriate watershed and climate stations were selected for model calibration, as well as for the project’s ultimate objective—determining the water supply capacity.

Drought analysis employing the Weibull distribution was conducted to determine the annual drought precipitation and water yield using the calibrated, long-term precipitation data and the long-term discharge output from the UBCWM.


8 363908C101_WB102008001VBC


4.2 Hydrology – UBC Watershed Model The UBCWM was developed at the UBC and is widely used in British Columbia to simulate stream flows from mountainous watersheds. Since the hydrological behavior of mountainous watersheds is a function of elevation, the model divides the watershed into several elevation bands and uses precipitation data and minimum and maximum daily temperatures as input. This calculated stream flow is the combination of rainfall, snowmelt, upper groundwater, and deep zone groundwater.

The model requires calibration using data from a climate station inside or close to the watershed and a hydrograph from the watershed outlet. Appendix A provides a more detailed description of the model and calibration process.

4.3 Hydrometric and Climate Station Climate Station Data from the valley meteorological stations may be useful for estimating runoff potential from the highest mountain slopes. The best data would be from high on the mountain slopes, but the majority of meteorological data is from valley stations. Long data series are required to obtain high-accuracy model outputs.

There are four Environment Canada climate stations with data series longer than 25 years close to the Comox Lake Watershed: Comox A (#1021830), Courtenay Puntledge BCHP (#1021990), Cumberland (#1022250), and Cape Lazo (#1021320). The locations of these stations are indicated in Exhibit 3-1.

Table 3-1 provides a summary of the characteristics of the four climate stations and the data series.

TABLE 3-1 Comparison of Climate Stations

Consecutive Data Series

Station ID Station Name Status

Elevation(m) From To

Total Years

Missing Data

1021830 Comox A Active 26 1944 2007 63 No 1021990 Courtenay Puntledge BCHP Inactive 24 1921 1964 43 A lot 1022250 Cumberland Inactive 159 1923 1977 54 A few 1021320 Cape Lazo Inactive 38 1935 1962 27 A few Note: The green marks the station used in this project

Climate station Comox A (#1021830) was selected for this project for the following reasons:

• Longer data series generate more reliable results. Comox A has the longest data series with no missing data, while Station Cape Lazo has the shortest data series (27 years, 1935 to 1962) and a few gaps in the data; Station Courtenay Puntledge BCHP has a lot of data missing; and Station Cumberland has a shorter data series (54 years, 1923 to 1977) than Station Comox A (63 years, 1944 to 2007).

• Distance to the watersheds used for calibration and validation. The model calibrates the precipitation data by applying a factor to it so that the simulated hydrograph agrees



with the observed one. To reduce the bias in model calibration involved with the similar watershed method, it is better to use a climate station that is approximately the same distance from the watershed used for calibration and the one used for application. Comox A is at a similar distance from the centroids of the Browns River and Comox Lake Watersheds (23 and 28 km, respectively).

Hydrometric Station Nearby hydrometric stations include Browns River Near Courtenay (#08HB025), for the Browns River, and Puntledge River Below Diversion (#08HB084), for the Puntledge River. The watershed discharging to this second station includes the entire Comox Lake and Perseverance Creek watersheds, but flow rates are influenced by controls for hydro power generation. The Browns River watershed was selected for the purpose of model calibration due to its similar watershed physiographic characteristics and available hydrometric station.

Exhibit 3-1 shows some of the watershed characteristics for the Browns River and Comox Lake Watersheds. Table 3-2 compares the characteristics of these two watersheds.

TABLE 3-2 Watershed Physiographic Characteristics

Elevation (m)

Watershed Hydro Station From To Avg. Area (ha) Slope

Distance to Climate Station Comox A

(km) Browns River 08HB025 100 1,400 858 10,407 0.114 23 Comox Lake 140 2,040 970 46,212 0.151 28

4.4 Drought Analysis Drought analysis was performed using the calibrated precipitation and water yield output. Two types of statistical distributions, Gumbel and Weibull, were tested to fit the data, and it was found that the Weibull distribution fit the data better than the Gumbel distribution.

Precipitation over the watershed and water yield were estimated with the UBCWM using the 63 years of data from climate station Comox A. The annual precipitation and water yield were calculated from the calibrated precipitation and the hydrograph output from the model for the period of July 1, 1944 to December 31, 2007.

There is no 100-year return frequency drought year in the historical records; however, the Weibull cumulative distribution is used to estimate this value in the Comox Lake Watershed. From an annual precipitation of 1,485 mm, the estimated water yield is 1,157 mm (Appendix B). This translates to an average drought-year flow rate of 16.88 m3/s.

Drought Period From the computed water yield, a critical drought period was selected for further use in the storage analysis. The critical period was selected based on the following criteria:

• The critical drought period is preceded by a wet year. • The critical drought period duration is longer than 1 year. • The critical drought period includes a year with water yield similar to that calculated for

the 100-year return period drought year. Exhibit 3-2 shows the average annual water yield for 1, 2, and 3 consecutive years.


10 363908C101_WB102008001VBC


This page left intentionally blank.


12 363908C101_WB102008001VBC


This page left intentionally blank.



EXHIBIT 3-2 Comox Lake Watershed’s Average Annual Water Yield

15

20

25

30

35

40

45

1940 1943 1946 1949 1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 2006 2009

Ave

rage

Ann

ual W

ater

Yie

ld (m

3 /s)

1-Yr Average WY

2-Yr Average WY

3-Yr Average WY

Average WY-Whole period

From Exhibit 3-2, the critical drought period selected was from 2000 to 2006.

Modification to the Drought Period The computed water yield for the critical drought period was modified using a linear factor to represent the 100-year return period drought year. At the same time, the data was extended using data from 1999 to reflect a wet year at the end of the period.

Exhibit 3-3 shows the original and modified data.


14 363908C101_WB102008001VBC


EXHIBIT 3-3 Drought Period Modification

14

16

18

20

22

24

26

28

30

32

34

36

38

40

42

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ave

rage

Ann

ual

Wat

er Y

ield

(m3 /s

)

OriginalModified

4.5 Water Yield The computed average water yield for an average year is 30.31 m3/s, and the average water yield for the critical drought period is 25.82 m3/s. Exhibit 3-4 and Table 3-3 show that the average monthly water yield in an average year, 100-year return frequency drought year and critical drought period is insufficient to meet water demand.



EXHIBIT 3-4 Comox Lake Watershed’s Average Monthly Water Yield

0

10

20

30

40

50

60

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Ave

rage

Mon

thly

Wat

er Y

ield

(m3 /s

)

Average YearDrought Period100- yr Return Frequency Drought YearLicensed Water Use & Fisheries Pulse Flows

TABLE 3-3 Comox Lake Watershed’s Average Monthly Water Yield

Month Average Year

(m3/s) 100-year Return Frequency

Drought Year (m3/s) Drought Period

(m3/s)

January 26.77 16.46 33.35 February 24.53 8.79 13.80 March 23.54 10.68 22.16 April 27.67 19.15 27.13 May 47.92 29.56 39.15 June 52.26 26.28 39.56 July 31.44 14.02 19.12 August 16.00 7.75 8.23 September 11.53 4.75 8.74 October 29.52 34.61 27.72 November 39.68 14.60 37.30 December 32.89 15.93 33.57 Average 30.31 16.88 25.82


16 363908C101_WB102008001VBC


4.6 Water Demand The amount of water licensed in the Comox Lake Watershed has increased over the past years. This study includes the major water users (BC Ministry of Environment, 2008) and pulse flows to support fisheries based on the Puntledge River Project Water Use Plan (BC Hydro, 2004). These are summarized as follows:

• BC Hydro uses water for power generation, which is diverted into the penstock at the Puntledge diversion dam at a maximum rate of 28.3 m3/s.

• CSRD uses 0.29 m3/s, which is taken either from the Penstock by gravity or from the Puntledge River by pumping, for the Comox Valley Water Supply System.

• Federal Department of Fisheries and Oceans (DFO) and BC Hydro use 5.7 m3/s, the minimum flow to be provided in the Puntledge river between the Diversion Dam and Browns River, for conservation purposes.

• Pulse flows required for the benefit of fish include the following:

− From January 15 to February 15: pulse flows of 12 m3/s, for four 48-hour periods, a minimum of 5 days apart

− From March 15 to April 15: pulse flows of 12 m3/s, for four 48-hour periods, a minimum of 5 days apart

− From July 2 to August 15: pulse flows of 12 m3/s, for five 48-hour periods, a minimum of 5 days apart

− From October 1 to October 31: pulse flows of 12 m3/s, for four 48-hour periods, a minimum of 5 days apart

4.7 Storage Analysis A storage model was developed to determine the water supply capacity of the Comox Lake Reservoir, where the input to the model is the water yield for the modified critical period, as described in Section 4.4.

Model Elements The key elements in the model are summarized as follows:

Reservoir Inflow The reservoir inflow is the water yield for the period between 1999 (wet year) to 2008 (wet year) and the 100-year drought year (2001) in between.

Storage Curve of Comox Lake Between its normal maximum and minimum operating elevations, Comox Lake has a storage capacity of approximately 94.2 million m3.

Exhibit 3-5 shows the elevation-storage relationship for the Comox Lake Reservoir



EXHIBIT 3-5 Comox Lake Reservoir’s Elevation-Storage Relationship

130

131

132

133

134

135

136

0 10 20 30 40 50 60 70 80 90 100

Storage (Mm3)

Elev

atio

n (m

)

Storage Curve Max Normal Operating Level 135.33 m Min Normal Operating Level 130.8 m

Outflows and Operating Controls The water release is based on water demand, operating conditions, and overflow through the spillway, and includes:

• Fisheries continuous minimum flow of 5.7 m3/s and pulse flows, as described in Section 4.6

• Continuous municipal water supply of 0.29 m3/s

• BC Hydro flow according to the reservoir water levels (WSEL):

If WSEL < 130.8 m, then BC Hydro flow is equal to 0 If 130.8 m ≤ WSEL ≤ 134 m, then BC Hydro flow is equal to 7 m3/s – If WSEL > 134 m, then BC Hydro flow is equal to 28.3 m3/s; maximum operating

capacity

• Spillway overflows when the WSEL in the reservoir ≥ 135.33 m

Water Balance Exhibit 3-6 shows the average monthly inflows, outflows, and water levels for the Comox Lake Reservoir during the period selected for storage analysis (1999 to 2008). This graph shows the reservoir has insufficient storage capacity; water yield from wet years could have been stored to supply water demand during dry periods if capacity were greater.


18 363908C101_WB102008001VBC


EXHIBIT 3-6 Average Monthly Water Balance Period, 1999 to 2008

0

20

40

60

80

100

Jan-99 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

Flow

(m3 /s

)

120

125

130

135

140

WSE

L (m

)

Inflows Outflow Lake WSEL



Exhibit 3-7 shows the average monthly distribution of the outflows for the various uses (overflow, BC Hydro, CSRD, DFO) from 1999 to 2008.

EXHIBIT 3-7 Average Monthly Water Supply Distribution Period, 1999 to 2008

0

10

20

30

40

50

60

70

80

Jan-99 Nov-99 Sep-00 Jul-01 May-02 Mar-03 Jan-04 Nov-04 Sep-05

Wat

er S

uppl

y (m

3 /s)

OverflowBCHydroCSRDDFO

The average monthly water balance analysis indicates that the portion of water supply that is available for hydro power, while providing base flow for sustaining fish habitat and continuous municipal supply, is largely dependent on the reservoir storage capacity.

From the average annual water yield for the period of 1999 to 2008 (28.48 m3/s), only 25.55 m3/s, or 89 percent, may be used for water supply due to the limited reservoir storage capacity.

5. References BC Hydro. 2004. Puntledge River Project Water Use Plan. http://www.llbc.leg.bc.ca/public/PubDocs/bcdocs/404112/environment30828.pdf. Accessed on October 8, 2008.

BC Ministry of Environment. 2008. Water Licenses Query. http://a100.gov.bc.ca/pub/wtrwhse/water_licences.input. Accessed on October 10, 2008.

CH2M HILL. 2006. Comox Lake Watershed Assessment − Summary Report. Comox Strathcona Regional District. June.

APPENDIX A

UBC WATERSHED MODEL AND MODEL CALIBRATION

WB102008001VBC/363908.C1 A-1 COPYRIGHT 2008 BY CH2M HILL • ALL RIGHTS RESERVED • COMPANY CONFIDENTIAL

APPENDIX A UBC Watershed Model and Model Calibration

A.1 Overview of UBC Watershed Model The UBC Watershed Model (UBCWM) was originally developed by Quick and Pipes (1977) at the University of British Columbia. It was developed to predict stream flows from mountainous watersheds where runoff is a combination of snowmelt, glacier melt, and rainfall. Dividing the watershed into several elevation bands, the model calculates daily watershed outflows using daily precipitation and maximum and minimum daily temperature as input. Since it was developed, the model has been further tested and improved and now incorporates many user-friendly features, as described by Quick (1995).

Since the hydro-meteorological behavior of mountainous watersheds is a function of elevation, the model uses the area-elevation band concept. This concept accounts for the orographic gradients of precipitation and temperature, which are assumed to behave similarly for each storm. The UBCWM also provides information on the area of snow cover, snowpack water equivalent, energy available for snowmelt, evapotranspiration and interception losses, soil moisture, groundwater storage, and surface and subsurface components of runoff. This information is available for each elevation band and can also be averaged over the whole watershed. The physical description of a watershed is given for each elevation band separately in the form of different variables, such as: band area, forested fraction and forest density, glaciated fraction, band orientation, and fraction of impermeable area. A schematic diagram representing the UBCWM structure is shown in Exhibit A-1 (Quick, 1995).

The UBCWM is made up of three major sub-models. The meteorological sub-model distributes the point values of precipitation and temperature ranges to all elevation zones within a watershed. The variation of temperature with elevation controls whether precipitation falls as rain or snow and also controls the melting of the snow pack and glaciers. The soil moisture sub-model controls the non-linear behaviour of the watershed and sub-divides the water input (rain and melt) into four components of runoff: fast (surface), medium (interflow), slow (upper groundwater), and very slow (deep groundwater). The routing sub-model allows the delivery of runoff to the outlet of the watershed and is based on linear reservoir theory that guarantees conservation of mass and water budget balance.

The UBCWM uses the energy balance approach to calculate snowmelt. The physical basis of the energy equation provides control when estimating snowmelt for the following: forested and open conditions, clear or cloudy weather, various slopes and aspects of mountainous watersheds, and changes in elevations. Because the detailed meteorological input required to drive the full energy balance equations is usually not available, especially for high, mountainous regions, the UBCWM drives the energy balance with just daily minimum and

APPENDIX A UBC WATERSHED MODEL AND MODEL CALIBRATION


maximum air temperatures. In this process, the different sources of energy creating the melt are estimated as a set of non-linear functions of temperature (Quick, 1995).

EXHIBIT A-1 Structure of UBC Watershed Model (Quick, 1995)



A.2 Model Calibration and Validation in Browns River The performance of the model with any set of input parameters is evaluated visually and statistically. The visual criterion involves plotting the simulated hydrograph and comparing it with measured flows. The statistical criterion involves the use of the Nash and Sutcliffe coefficient of model efficiency (Ce) and coefficient of determination (Cd), and the percent in volume difference (DV%). The coefficient of efficiency describes how well the volume and timing of the simulated hydrograph compares to the observed hydrograph. The coefficient of determination measures how well the shape of the simulated hydrograph reflects the observed hydrograph and depends solely on the timing of changes in the hydrograph.

The Browns River watershed was used for the purpose of model calibration. The hydrometric station, Browns River Near Courtenay (#08HB025), has discharge data in the following consecutive periods: February 1, 1960 to September 25, 1971 and January 1, 1985 to Present (Environment Canada, 2008). Considering that consecutive climate data is available at Station Comox A from 1944 to 2007, the period selected for model calibration is from 1988 to 2003 (15 years). Table A-1 shows the results of calibration.

TABLE A-1 Results of Model Calibration

Period Calibration or

Validation From To Years Ce Cd DV %

Total 1988 2003 15 0.65 0.65 8

Comparison of observed and simulated hydrographs are shown in Exhibit A-2. The monthly average discharges are compared in Exhibit A-3.



EXHIBIT A-2 Observed and Simulated Hydrograph Comparison

0

20

40

60

80

100

120

140

160

10/1/

1998

11/1/

1998

12/1/

1998

1/1/19

99

2/1/19

99

3/1/19

99

4/1/19

99

5/1/19

99

6/1/19

99

7/1/19

99

8/1/19

99

9/1/19

99

DATE

FLO

W (m

3 /s)

0

40

80

120

160

200

240

280

320

RA

INFA

LL+S

NO

WM

ELT

(mm

)

Snowfall+Snowmelt Observed Simulated

0

20

40

60

80

100

120

140

160

10/1/

1999

11/1/

1999

12/1/

1999

1/1/20

00

2/1/20

00

3/1/20

00

4/1/20

00

5/1/20

00

6/1/20

00

7/1/20

00

8/1/20

00

9/1/20

00

DATE

FLO

W (m

3 /s)

0

40

80

120

160

200

240

280

320

RA

INFA

LL+S

NO

WM

ELT

(mm

)


Browns River – 1999




EXHIBIT A-2 Observed and Simulated Hydrograph Comparison (continued)

0

20

40

60

80

100

120

140

160

10/1/

2000

11/1/

2000

12/1/

2000

1/1/20

01

2/1/20

01

3/1/20

01

4/1/20

01

5/1/20

01

6/1/20

01

7/1/20

01

8/1/20

01

9/1/20

01

DATE

FLO

W (m

3 /s)

0

40

80

120

160

200

240

280

320

RA

INFA

LL+S

NO

WM

ELT

(mm

)


0

20

40

60

80

100

120

140

160

10/1/

2001

11/1/

2001

12/1/

2001

1/1/20

02

2/1/20

02

3/1/20

02

4/1/20

02

5/1/20

02

6/1/20

02

7/1/20

02

8/1/20

02

9/1/20

02

DATE

FLO

W (m

3 /s)

0

40

80

120

160

200

240

280

320

RA

INFA

LL+S

NO

WM

ELT

(mm

)






EXHIBIT A-2 Observed and Simulated Hydrograph Comparison (continued)

0

20

40

60

80

100

120

140

160

10/1/

2002

11/1/

2002

12/1/

2002

1/1/20

03

2/1/20

03

3/1/20

03

4/1/20

03

5/1/20

03

6/1/20

03

7/1/20

03

8/1/20

03

9/1/20

03

DATE

FLO

W (m

3 /s)

0

40

80

120

160

200

240

280

320

RA

INFA

LL+S

NO

WM

ELT

(mm

)


EXHIBIT A-3 Monthly Average Discharge Comparison

Monthly Average Flow (1988-2003)

0

2

4

6

8

10

12

JAN

FEBMAR

APRMAY

JUN

JUL

AUGSEP

OCTNOV

DEC

ANN MEAN

FLO

W (m

3 /s)

ObsEst



A.3 Model Verification in Comox Lake Even though there is no observed flow data available for Comox Lake, there is a table estimating mean monthly inflows computed by BC Hydro based on a computer program called FLOCAL. These values are reported in Appendix 1 of the Puntledge River Project Water Use Plan (BC Hydro, 2004). Exhibit A-4 shows a comparison of the flows from the UBCWM for Comox Lake Watershed using the calibration parameter and the estimated values from BC Hydro using FLOCAL.

EXHIBIT A-4 Comparison of UBC Model Output with BC Hydro FLOCAL Estimation

Monthly Average Flow (1963-1999)

0

10

20

30

40

50

60

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC ANNMEAN

FLO

W (m

3 /s)

Puntledge Use Plan

UBC

A.4 References BC Hydro. 2004. Puntledge River Project Water Use Plan. http://www.llbc.leg.bc.ca/public/PubDocs/bcdocs/404112/environment30828.pdf. Accessed on October 8, 2008. Environment Canada. 2008. National Climate Archive. http://climate.weatheroffice.ec.gc.ca/advanceSearch/searchHistoricData_e.html?timeframe=1&Prov=BC&StationID=145&Year=2008&Month=9&Day=17. Accessed on October 9, 2008. Quick, M.C. 1995. “The UBC Watershed Model.” Computer Models of Watershed Hydrology. Vijay P. Singh, ed. Water Resources Publications. Quick, M.C., and A. Pipes. 1977. “UBC Watershed Model.” Hydrological Sciences Bulletin. Vol. 22. pp. 258-295.

Quick, M.C., and Z. Micovic. 1999. “A Rainfall and Snowmelt Runoff Modeling Approach to Flow Estimation at Ungauged Sites in British Columbia.” Journal of Hydrology. Vol. 226. pp. 101-120.

APPENDIX B

PLOTS OF DROUGHT ANNUAL PRECIPITATION AND WATER YIELD

WB102008001VBC/363908.C1 B-1 COPYRIGHT 2008 BY CH2M HILL • ALL RIGHTS RESERVED • COMPANY CONFIDENTIAL

APPENDIX B Plots of Drought Annual Precipitation and Water Yield

For this project, both Weibul and Gumbel statistical distributions were used for the drought analysis. It was found that the Weibull distribution was better suited for this analysis using the calibrated annual precipitation and water yield. Design drought annual precipitation and water yield are shown in Exhibits B-1 and B-2.

EXHIBIT B-1 Comox Lake Watershed – Precipitation

APPENDIX B PLOTS OF DROUGHT ANNUAL PRECIPITATION AND WATER YIELD

WB102008001VBC/363908.C1 B-2 COPYRIGHT 2008 BY CH2M HILL • ALL RIGHTS RESERVED • COMPANY CONFIDENTIAL

EXHIBIT B-2 Comox Lake Watershed –Water Yield

Documents

RWS Comox Lake Hydrology Final