R. R. Walker and R. W.
Tossell, Beak Consultants Ltd, Guelph, Ont.
View / Download Final Report [2525 KB pdf] (265 p, with appendices)
The purpose of the
hydrology component of PWS was to monitor
runoff and stream flow to determine if the implementation of
conservation farm systems had an affect on the overall basin hydrology.
The specific objectives relating to the hydrology component of the PWS
monitoring, establish continuous records of watershed water balance in
order to investigate hydrologic process;
determine the flow
component of runoff necessary for estimating mass flux of water
quality parameters; and
relationships between soil conservation systems and hydrologic
response at the plot, field and watershed scales.
microbasins were instrumented with flow monitoring and water quality
sampling devices to facilitate the accurate estimation of mass loadings
of water quality parameters. In-stream water control devices (v-notch
and rectangular weirs) were installed to better define low flow
estimates. Water quality shelters were installed at each watershed
outlet (two per study area, six in total) to house automated water level
monitoring, meteorological, and water quality sampling equipment.
Continuous water level data was used in conjunction with flow velocity
determination to derive flow-discharge curves for each watershed outlet.
The resultant continuous flow record was ultimately used for calculating
relationships between flow and water quality concentrations for water
quality loading determination.
A total of twelve
microbasins (four per study area) were instrumented with automated water
level monitoring equipment and manual water quality sampling which were
operated during non-winter months. Hydrologic control structures
(v-notch weirs and Parshall flume) were installed at each microbasin
along with a stilling well for water level-flow estimation purposes.
techniques were employed to evaluate water quality at the plot scale at
critical times of the year when soil conditions may vary due to farm
management or seasonal influences (ie. post-fall tillage 1990-91; spring
pre-plant 1991-92; and post harvest 1991). Water quality samples were
collected in triplicate from three field plots at benchmark sites in
both the test and control watersheds to determine water quality loads.
One pathway for
phosphorus loss is through subsurface soils and groundwater transport.
To define the magnitude of this pathway, groundwater monitoring wells
were installed in each watershed to determine the amount of phosphorus
was transported through the subsurface in the soluble phase. One
groundwater monitoring well was installed near each microbasin of each
study area. Groundwater samples were collected approximately monthly
through the monitoring phase of the study.
Results and Discussion
Essex control unit area
runoff slightly exceeded test runoff over the period of study.
Kettle Creek test unit
area runoff exceeded control runoff during the wettest seasons.
Pittock test unit area
runoff was significantly greater (nearly 50%) than that of the control
throughout the study period.
Frequency and extent of
microbasin flow was quite variable in all microbasins.
microbasins produced less runoff than test microbasins, especially
during periods of tillage.
Time to ponding (TTP)
values, indicating soil porosity, showed no distinct trends when
comparing test and control sites, possibly due to spatial variability
of infiltration rates of soils.
Time to runoff (TTR)
values, reflecting soil storage capacity, were not significantly
different for test or control sites, again possibly due to high
spatial variability of soil properties .
Total runoff volume was
generally higher for test sites than for control.
Runoff volume was
lowest for control sites following tillage, likely due to increased
The difference between
test and control runoff volume is most pronounced during pre-plant and
post-tillage, when the difference in surface cover is most pronounced.
The following are general
conclusions drawn from the PWS concerning hydrology.
At the watershed scale,
the effects of conservation tillage on runoff volume are site
Essex: runoff is higher
from the test watershed due to higher resultant cover in the last 2
years of the study.
Kettle Creek: runoff is
higher from the test watershed during the periods of high annual
Pittock: the test
watershed produced significantly higher unit area runoff volumes
throughout most of the study period.
At the microbasin
(field) scale, there is no clear pattern of dependency between unit
area runoff and conservation farm management in Kettle or Pittock. In
Essex, microbasins generally indicate that increased cover resulting
from conservation systems correlates with increased runoff.
At the plot scale,
responses of runoff to the presence of conservation tillage increased
cover corresponds to increased runoff in Kettle and Pittock, but in
Essex the reverse is true.
simulation, test runoff exceeded control when all data were analyzed
simulation, control runoff was lowest during the post-tillage period,
most likely due to high surface storage.
More replication is
recommended for plot scale studies, such as rainfall simulation
experiments, to reduce the effects of spatial heterogeneity of soil
At the microbasin
scale, greater duration of study is required so that more events are
available to be used in time trend analysis on individual microbasins.
Currently, direct comparisons between different microbasins are
confounded by differences in physical and agronomic factors, despite
all efforts to avoid such differences when choosing microbasins.
At the watershed scale,
extension of the duration of study to create a larger database would
help to more clearly define the effects of tillage and residue on
Thursday, May 19, 2011 07:37:36 PM