The social connectivity of urban rivers

By social connectivity we refer to the communication and movement of people, goods, ideas, and culture along and across rivers, recognizing longitudinal, lateral, and vertical connectivity, much as has been described for other riversfor hydrology and ecology. We focus on rivers as they pass through cities, and the relationships between these rivers and city dwellers. Historically, the most important longitudinal connectivity function of rivers was their role as major transport routes and the simplification of formerly complex, irregular banks and beds, into straight, uniform shipping channels has resulted in a loss of lateral and vertical connectivity, notably the quotidian uses such as fishing, washing clothes, water supply, swimming and other recreation. The scale of the river itself, and its scale in comparison to the scale of the city, largely determine the river's social function and the degree to which it influences city form. River width affects the perception of 'closeness' of the other bank, ease of bridging the river, influence of the river on the city's street pattern, and type of waterfront uses that occur. Up to 15 m wide, people can converse, whereas across rivers similar to 50 to similar to 200 m wide, people are not recognizable but still clearly visible, instilling the banks with a 'lively' atmosphere. At widths over similar to 200 m, people blur, yet moving vehicles and trees branches shaldng in wind may still provide some dynamic elements to an otherwise static landscape composed of building facades. In exceptionally wide rivers, the city on the opposite bank is little more than a skyline, which often becomes a signature and symbol of regional identity. In contemplating how people use rivers, we can define a range of human activities in relation to height above the water (i.e., instream to banktop), a vertical dimension of human connectivity with rivers. Many uses occur on the top of the bank, such as quiet contemplation, walking, or cycling along a riverside trail, while others depend on contact with the water itself, such as wading, diving, and canoeing (which presupposes adequate water quality). Many of these relationships are illustrated by the challenge of reconnecting Cairo with the Nile. (C) 2016 Elsevier B.V. All rights reserved.