Most likely the underlying reason for the grounding - pilot error/experience. Pilots are required to be on board, and most likely the pilot encountered a traveling and swirling 'eddy(s)' along the banks AND especially at the bend where the two channels intersect.... and misjudged. These large swirling eddies are VERY common in this section of the Delaware River during the early spring thaw due to the massive amounts of water (and mud) being released from the melting of the snow pack in the Pocono Mountains. This is not the first time a large bulk carrier has been 'turned' by a large eddy in this stretch of river. When the large steel mill in this area was active, several bulk carriers became grounded this way in the 50s and 60s.
The Delaware River from this section, on north to the New York border, is 'novel' in its hydraulic flow characteristics. Its essentially a shallow Vee bottomed river and it 'pulses' depending on the variable drainage happening all the way north to its headwaters in New York state. The river is navigable / tidal all the way to the city of Trenton (about 5 miles north of this grounding); the tide goes no further north than the 'Trenton Falls' ... a low rapids strewn with boulders (best 'fishing hole' on the entire river .... stripers!!!!!). The tide depending on wind/flow conditions 'can' be as much as 4-6 ft. A high tide will back up water well north of the 'falls' and when the tide 'turns' will release that water, depending on how much is backed up and the variable and 'pulsing' volume coming down during early springtime, and can set up quite large swirling 'eddys' that drag along the banks. During my high school years I actively fished this section for white perch, & spawning striped bass, herring, and American Shad; I used to know and favor where these eddies formed just after the tide change, ..... especially during 'the thaw'.
At this time of year - during the THAW (and breaking ice dams) - the river flow is quite variable, a cold day will slow the flow considerably and a warm day or a breaking ice dam (freshet) up-river can spectacularly increase the flow during 'the thaw' in early spring.
This year because of the massive and unusually high snow pack in the mountains, the river is variably flowing at up to 3 to 5, or more, times normal volume (
National Weather Service Advanced Hydrologic Prediction Service). On top of all this, if there was a strong SE blow on the Delaware Bay, it will stop the tide and back up water all the way from near Cape May to well beyond the Trenton Falls .... but the flow keeps coming from the mountains AND when the tide finally turns ... it can be like someone flushed a BIG toilet. The C&D canal (lower down on the Delaware River near Wilmington Del.) is affected the same way; and, the currents in both the Delaware and C&D are 'hydraulic' - not based on 'normal tidal' changes but on how the water flows through all its 'choke points'.
In all probability the pilot wasnt 'used to' the the large 'eddies' traveling and spinning along the banks and bends during early springtime; and / or, got caught between two large spinning eddies that affected the water velocity differently along each side of the ship and thus was 'forced' into a turn. For the past 20 years our winters have been increasingly mild and the snow pack in the mountains has been scant. Since about 2004-5 the climate (here) has been changing back to 'normal', especially since 2009. The winters of 2013, 2014 & 2015 have been especially 'brutal' in the Pocono Mountains and with quite very deep snow pack (.... all thanks to the return of global cooling). ;-)
The Delaware River 'quiets down' after the late winter / early spring 'run offs' and freshets and with the exception of occasional heavy rains in the mountains at other times, stays 'predictable' for the rest of the year.
This ship probably got caught in a large swirling eddy during the early spring 'run off'. Such groundings were not all that rare, 'in the old days'.