Analysis of Streamflow Trend in the Susquehanna River Basin, USA - Hydrologic Time Series Analysis: Theory and Practice - page 196

times can be used to detect the trend pattern. In this study, the graphical
representation of the multiple trend tests was used to aid in the detection of
changes in the streamflow time series. This methodology (computational and
graphical) was applied to 11 selected watersheds distributed across the
Susquehanna River Basin of the United States.
The analysis of the results of this study indicated that the four watersheds
located in the Appalachian Plateau experienced a step increase around 1970 in
the annual median flow and annual minimum flow, while the four watersheds
located in the Valley and Ridge experienced a step increase around 1970 in the
annual minimum flow. However, none of the watersheds experienced a step
increase in the annual maximum flow. The trend changes are seen to be
geographically arranged with the greatest change at inland locations, and with
the amount of change decreasing toward the Atlantic coast. The abrupt step
increases around 1970 occur in the summer and fall seasons, which are usually
characterized by low flows in the Susquehanna River Basin (SRB). This is
consistent with the step increase in annual minimum flow in most of the
watersheds under study. This implies that there has been an increase in the
amount of recharge received by aquifers in the SRB during low flow months
in the Appalachian Plateau and valley and ridge.
Overall, it can be concluded that the methodology of multiple Mann-
Kendall tests with varying beginning and ending times, and the graphical
interpretation of the results, as demonstrated in this study, are valuable screening
tools for the detection of trend patterns in hydrologic time series. Although the
SRB is not a geographically large basin, the watersheds within this basin still
show varying trend patterns which indicate that fine spatial resolution trend
analyses may be warranted.
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