Observation Well Information

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Introduction

The Province operates a network of observation wells to provide data on ground water level fluctuations and ground water quality information on developed aquifers in British Columbia. Observation well water levels are monitored using one of four methods: 1) manually with a wetted tape, 2) continuously using Steven's chart recorders, 3) electronically with data loggers or 4) remote monitoring using cellphone technology.

Water level data from observation wells are collected on a monthly basis by field observers and forwarded to Regional Offices. Data are then checked for errors and ommissions and forwarded to the Water and Air Monitoring and Reporting Section for final checking and storage. Water level data are referenced from ground level and the month end water level reading are entered and stored in Excel to produce a month-end hydrograph. The method of measurement and accuracy of each method are given below:

Method of measurement Accuracy
Wetted Tape Method +/- 1 mm
Steven's Chart Recorder +/- 1 mm
Data Logger +/- 0.1 %

Williams Lake Observation well hydrograph

Hydrograph Analysis - Observation Well 261

The graphs above compare the observation well ground water level hydrograph (top graph) with the cumulative precipitation departure (CPD) graph (middle graph) and monthly precipitation totals for the period of monitoring (bottom graph). CPD graphs are useful for assessing how precipitation affect ground water level fluctuations in shallow unconsolidated aquifers. CPD graphs are attained by plotting the cumulative departure from the mean monthly precipitation mean for the period of monitoring. CPD graphs provide a valuable understanding to how ground water levels in a particular aquifer responds to precipitation recharge.

Observation well 261 is completed in fractured bedrock to a depth of 79m (260 ft) and is overlain by a thick sequence of clay and gravel layers to a depth of 71m (233 ft). The ground water level in the well ranges from a high of 23.75m to a depth of 27.5m below ground level. Comparison of the observation well hydrograph and the CPD graph between the period 1980 and 1987 suggest there is a good relationship between the CPD fluctuation and the ground water level fluctuation at this location. Seasonal water level fluctuation in the hydrograph is somewhat subdued. The subdued water level fluctuation is likely due to the fractured bedrock being slow to recharge or the thickness of the overburden may be dampening out any seasonal effects from precipitation because of thick sequences of confining clay overlying the bedrock. The CPD curve is lowest in February or March 1988 and the ground water level reached a historic low in February or March 1991. Although the CPD curve rises between early 1988 and late 1990 precipitation remains below average which is reflected in the ground water level continuing to decline during this 3 year period. Between 1987 and mid 1996, precipitation was below average resulting in the ground water level rising between early 1991 and late 1993 likely a reflection of the rising (although below average) water level in the hydrograph between early 1988 and late 1990. The above average precipitation that occurs in late 1996 shown in the CPD curve is reflected in the rising ground water level measured in late 1997 and early 1998. The below average precipitation in 1998 to 2000 is again followed by a declining ground water level in the observation well.

 


NOTE* Detailed water level information for this well is available in Excel Format.
For more information, please email
groundwater@gov.bc.ca