No, there is also flood control via reservoirs on the tribs and, if it was implemented, enhanced flow for mussels.
I have never seen much in-stream scouring along the Delaware. The evidence of that is that the gravel bars with which I have been familiar have not appeared to grow very much over the years. On the other hand, the island and shoreline vegetation periodically gets pretty ripped up. As for sediment deposition, it is primarily sand and seems to primarily get deposited in back eddies.
I almost said that the main river bottom substrate is pretty stable because I was thinking about all of the cobble substrate throughout much of the river except around some split channels, but then I recalled the wide, shallow, gravelly areas from Point Pleasant to the head of tide.
I would not just focus on sediment deposition and scouring being problematic for nesting SMB, however. Higher spring flows from periodic storm events = falling water temps, which when they fall enough will cause SMB to abandon the nests. These events will also cause pH to fall, but I have never read any discussion of that regarding SMB fry survival as I have regarding Striped Bass fry survival in the Delaware Estuary.
I would add that the lower Susquehanna, which I covered along with the lower Delaware and Schuylkill, had much more of a sedimentation problem than the Delaware. There is really no comparison in that regard.
As for fertility, there is continuous loss of nutrients in a downstream direction in all systems, but those with anadromous fish species that perish in great part ( American shad in this case) post-spawn regain substantial amounts of nutrients from the ocean as they decompose. Tangential to this, yet interesting, is that in Alaska the vast majority of nutrients in many streams have decaying salmon as their source.
