HAER Report

Preparing the River

Restoring good drainage conditions along the Bronx River was essential for successful parkway development. Without a program to regulate the river, the parkway would always be subject to inundation. Regulating the river to control flooding had always been a difficult proposition due to the numerous landowners and municipal jurisdictions along it. Since the BPC controlled the entire reservation along the river, it was able to develop a comprehensive plan to regulate the watercourse. In 1917, the commission began a comprehensive construction program to drain, grade, and sometimes reroute the river in preparation for park and road construction.

To achieve a good foundation for the parkway drive, Downer explained that it was necessary to drain the river and grade alongside it. The river and adjoining land were almost at the same grade, which meant that the bottomlands were too wet to serve as a stable road foundation and subject to frequent flooding. Either the marshy wetlands had to be raised by fill, or the river had to lowered, or both actions had to be taken in concert. The cost of bringing in fill to raise the adjacent bottomland would have been extremely expensive, so the decision was made to lower the river. The river would be lowered by dredging it to deepen the channel, by removing obstructions, and where necessary, by lowering the crests of existing dams. By lowering the river’s water level, the BPC would reduce the risk of flooding and lower the water table of adjacent lands. The BPC conducted hydrographical surveys that collected stream-flow data and gauge-height records from the Bronx River. Flow volumes were recorded and minimum and maximum flow were determined.(171) Downer calculated that successful flood regulation would require dredging the river to a depth of 3' below the existing low water level. He estimated that more than 150,000 cubic yards of material would have to be dredged from the river bottom.(172) To further reduce the danger of flooding and provide a more solid base for parkway development, a substantial amount of fill was spread on low-lying areas. Fortunately, the dredging process provided an ample source of excavated material to accomplish this task. Material excavated from the river was used to fill in low marshy areas and provide a well-drained subgrade for the roadbed. BPC engineers aimed to achieve an efficient balance between the materials dredged and the quantity of fill needed for raising the adjacent land. For every foot that the river was lowered, the equivalent of a foot of fill was spread on the adjoining bottomlands.(173)

Merkel pointed out that the extensive dredging, filling, and channelization efforts had a number of benefits beyond the obvious goal of draining swamps and controlling floods. Deepening and widening the river channel created better opportunities for activities such as bathing and canoeing. The recreational and aesthetic appeal of man-made lakes and ponds was obvious, but they often had subtle practical benefits as well. Water features could be used as a means of generating fill for other uses or accommodating excess material from areas being excavated for parkway development. Lakes and ponds could be scooped out of the river in areas where additional fill was needed. In the case of Bronxville Lake, Merkel raised the surrounding area to accommodate 10,000 cubic yards of fill generated from excavations related to the construction of grade separations at Palmer Road and Swain Street. The river channel was also relocated to facilitate the design and construction of the parkway drive. The river could be moved out of the way in areas where the original stream course conflicted with the designers’ intentions and manipulated to enhance the view from the parkway’s roads and paths.(174)

Construction Begins

Preparing the River