Watershed Conservation Plan - Destination Erie

via the Erigan River, a major river system that flowed east through the present-day Lake Erie and Lake
Ontario basins and the St. Lawrence Lowlands.
At this time, however, Lake Erie did not exist and the Allegheny-Ohio River system had not assumed
its present form. Instead, as Tomikel and Shepps (1967) note, northwestern Pennsylvania and northeastern
Ohio were drained by three discrete "Allegheny" systems (Figure 2.6) that flowed north through New York,
Pennsylvania, and northern Ohio, unlike the Allegheny system's present-day southward flow. The
northernmost of these systems is the only one of these systems that is thought to have traversed the study area,
specifically in the general vicinity of Elk and Conneaut Creeks. The catchment area of this ancient river was
much larger than that of those present-day creeks, and ca. 18,000 B.P. it probably extended well to
south—perhaps as far as northern Butler County, some 125 km (77.5 mi) south of present-day Lake Erie's
southern shore. The ancient stream corresponding to present-day French Creek drained southward into the
ancient "Middle" Allegheny River, which in turn flowed south (past present-day Oil City and Franklin) until
turning northwest in the vicinity of Meadville. From there it flowed to northwest into the Erie basin in the
vicinity of present-day northeastern Ohio. The deep valley that carried this stream has been partly or
completely obliterated by glacial filling [Tomikel and Shepps 1967:48–50].
As successive ice lobes crossed
northwestern Pennsylvania, the existing valleys
like those described above were either nearly or
completely filled with sediments, effectively
obliterating the pre-glacial drainage network. As
the ice lobes reached their maximum southern
extent and began to melt, large quantities of
water were produced, filling the valleys in front
of the ablating ice sheets and creating a major
south-draining river system. As the edge of the
ice receded, there formed in front of the ice a
lake whose water levels were controlled by the
elevation of outlets where available. The
recession of the glacial ice into the Erie Basin
formed a large lake, named ancestral Lake Erie,
that drained westward through an outlet down
the Wabash River. With the continuing eastward
and northward retreat of the ice, successive
lower outlets were created and the sudden
opening of new outlets caused ancestral Lake
Erie to rapidly fall to new levels. As a result, a
series of strand lines or beach ridges developed
around the margin of the lake, with the older
beach ridges occupying a higher topographic
position. The successively older lakes in the
Erie Basin that may have existed in Erie County
are listed in Table 2.2 from youngest to oldest,
with the approximate height of their surface
tread (Tomikel and Shepps 1967:50–51).
As noted by Calkin and Feenstra (1985)
and Thomas et al. (1987), the Lake Erie basin
Figure 2.6. Schematic configuration of the three discrete
"Allegheny" systems that flowed north through New York,
Pennsylvania, Northwestern West Virginia, and
northeastern Ohio: (1) upper, (2) middle, and (3) lower
(adapted from Tomikel and Shepps 1976:Figure 34).
14
has been occupied by a series of major
proglacial ice- or moraine-dammed lakes and
non-glacial lower-level lake phases since late
Wisconsinan times. These lakes and lake phases,
which formed as the Ontario-Erie ice lobe
retreated and subsequently moved in response to