  This study investigates flood avalanches in a dense reservoir network in the
semiarid north-eastern Brazil. The population living in this area strongly
depends on the availability of the water from this network. Water is stored
during intense wet-season rainfall events and evaporates from the reservoir
surface during the dry season. These seasonal changes are the driving forces
behind the water dynamics in the network. The reservoir network and its
connectivity properties during flood avalanches are investigated with a model
called ResNetM, which simulates each reservoir explicitly. It runs on the basis
of daily calculated water balances for each reservoir. A spilling reservoir
contributes with water to the reservoir downstream, which can trigger
avalanches affecting, in some cases, large fractions of the network. The main
focus is on the study of the relation between the total amount of water stored
and the largest observable cluster of connected reservoirs that overspill in
the same day. It is shown that the thousands of small and middle-sized
reservoirs are eminent for the retention of water upstream the large ones.
Therefore, they prevent large clusters at a low level of water. Concerning
connectivity measures, the actual reservoir network, which evolved without an
integrated plan, performed better (i.e., generated smaller avalanches for
similar amount of stored water) than numerous stochastically generated
artificial reservoir networks on the same river network.
