The impact of urban groundwater upon surface water - eTheses ...

MONITORING NETWORKS AND METHODS
The method of data collection followed was as outlined by (Dingman, 1994). A measuring
tape was stretched across the channel and fixed to each bank. Measurement points were
spaced at 0.5 m intervals across the channel and the depth was recorded at each location. Flow
velocity measurements were taken for each point at a depth of 0.6 m*(total depth) as previous
workers (Clay, 1999, Cey et al., 1998) have found that this is representative of the average
flow rate over the total depth. A fixed point was chosen to act as a stage reference mark. The
river stage was taken at the beginning and end of the profile measurement to give an
indication of any variation in discharge from upstream that may have occurred during the
course of the profile measurement.
Because of time constraints it was not possible on every occasion to repeat the velocity
measurements back across the profile so as to obtain an estimation of the measurement
repeatability. However, for the readings taken on May 21 and repeated on May 22, 2001,
there is good correlation, indicating that the method shows good repeatability. The digital
flow meter provided an average velocity over a one minute period from readings taken at one
second intervals which reduced the error from this source. Error estimates of +/- 15 % are
indicated by Cey et al, (1998) under similar conditions.
The data were analysed using the mid-sectional method to estimate the total discharge across
the profile. The total discharge for each profile was then plotted against distance down river to
give an indication of the discharge accretion. Discharge measurements taken on six different
days were combined with other available data (Clay, 1999, Knowles, 2000) to provide an
indication of the variability of baseflow discharge accretion along the study reach.
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