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 %|
Hydrograph Analysis - Observation Well 259
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 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 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 259 is completed in a confined aquifer (Whonnock Aquifer #26). The ground water level in the well range from a high of close to ground level (0 m) to a depth of over 1.7 m (5.6 ft) below ground. The hydrograph indicates that maximum ground water levels in this well occur seasonally during the period March to May and minimum ground water levels occur during September and October. Pumping interference is also evident on the monthly water level charts but that detail can not be seen on the above hydrograph. The hydrograph also shows that ground water level fluctuations have year-to-year cycles in addition to the seasonal cycles. For example, ground water levels are generally higher between 1981 and 1987 and between 1997 and 1999.
The cumulative precipitation departure (CPD) curve shows similar seasonal fluctuations preceding the ground water level fluctuations by about two months. The annual cyclic fluctuation in response to precipitation in both the CPD curve and observation well fluctuation shows close similarity throughout the 20 year monitoring period. The years 1982 to 1987 were years of above average precipitation and correspond with generally higher ground water levels. Average precipitation decreased in 1987-1988 and between 1993 and 1995 and a corresponding decrease in ground water levels is evident. Between 1996 and 1999, average precipitation increased and ground water levels increased in response.
The comparison of the
ground water hydrograph and CPD curve and monthly total precipitation graph shows
that a significant portion of the recharge to this aquifer appears to be derived
from precipitation falling in the local area.