Hydromorphological effects of the renaturalization of an urban river: the Manzanares River in the city of Madrid (Spain)

Abstract

As is the case of most rivers in large cities, the Manzanares River in the city of Madrid was channelizedwith rip-rap and stone walls to allow for intensive urban development. Moreover, nine small control damswere built for aesthetic reasons so as to maintain a view of a large river. At the ecological level, themargins were disconnected from the channel by artificial structures, and the longitudinal connection offlows, sediments and species between upper and lower sections was greatly diminished. The openingof the urban dam gates, in May 2016, has been the first step towards the renaturalization of the river.Renaturalization objectives include recovering the key function of the river as ecological corridor(connecting the river sections upstream and downstream of the city) and enhancing the landscape andsocial value of the river within its urban context. The first ecological effects of the longitudinalreconnection of 7.5 km of urban river can be assessed in terms of partial recovery of hydromorphologicaldynamics. Firstly, by eliminating water retention, water depths have lowered from around 4 m averageto 0.3 m, allowing for more natural water flows, shallower and with different velocities within the channel.Secondly, sediments, mainly sands, from upstream tributaries are entering the fluvial system and arebeing deposited in the channelized section, creating lateral bars and islands. The case of theManzanares River can help in understanding how an urban river can evolve with a non-intensiveintervention focused on self-forming dynamics recovery.