While large-scale transverse drainages (TDs) such as those of the Susquehanna River above Harrisburg, PA, have been recognized since the 19th century, there have been no systematic surveys done of TDs since that of Ver Steeg's in 1930. Here, the results are presented of a topographic and statistical analysis of TDs in the Susquehanna River basin using Google Earth and associated overlays. 653 TDs were identified in the study area, 95% of which contain streams with discharges of less than 10 m3/s. TD depths ranged from a 23 m deep water gap near Blain, PA, to the 539 m deep gorge of the Juniata River through Jacks Mountain. Although TD depth tended to increase with stream size, many small streams were located in deep gaps, and eight streams with discharges of 10 m3/s or less were found in gorges whose depths matched or exceeded the deepest TD of the Susquehanna, the largest stream in the basin. Streams of less than 10 m3/s made up the majority of TDs regardless of the rock type capping the breached structure. Overall, TDs through sandstone-capped ridges were deeper than those topped by shales, and TDs in both sandstones and shales displayed a lognormal distribution of depths, which may be indicative of a preferred value. Stream flow direction was primarily perpendicular to local structural strike, with 47% of streams flowing NW and 53% flowing SE. 19% of the TDs were found to be in alignment with at least one other TD, with aligned segment lengths ranging from .5 to 14.8 km. The majority of TDs were in rocks of Paleozoic age. The techniques described here allow the frequency and distribution of TDs to be quantified so that they can be integrated into models of basin evolution.

For detailed maps and elevation profiles of each site see "Further details:"Columns 12-15 refer to elevation data gathered from S-profiles drawn in Google Earth over transverse drainages (TDs) (see fig. 1a, attached). As shown in the article, S-profiles are useful for identifying TDs because they exhibit a typical M-shaped elevation over TDs, while S-profiles over normal channel segments exhibit a more irregular pattern.Column 12 refers to the general elevation of the upstream leg of the S-profile over the TD.Column 13 is the elevation of the highest point of the highland breached by the TD.Column 14 refers to the base level of the stream channel in the segment of the S-profile crossing the breached ridge.Column 15 is the difference between Cols. 13 and 14, which is used as a proxy for TD depth (see second Fig. 1a for graphical explanation).

Supplement to: Lee, Jacqueline S (2012): Transverse drainages of the Susquehanna River basin, Pennsylvania, USA. Geomorphology, 186, 50-67