26. Voluntary Agreement for River Regime Restoration Services in the Ebro River Basin (Spain)

The construction of the Mequinenza and Ribarroja dams back in the 1960s modified the hydrology and changed the physical and environmental conditions of the Lower Ebro River in northeastern Spain. These conditions have stirred the uncontrolled proliferation of macrophytes, which have become a relevant concern in the area since 2000. Among other environmental and economic impacts, macrophytes threaten hydroelectric power infrastructures, increasing operating costs and reducing the productivity of power-generating plants. Macrophyte blooms thus became the catalyser for collaboration between the hydropower operator and the Ebro River Basin Authority, within a larger consortium with academic experts on floods and sediment flows, to deliver controlled water floods (flushing flows). The economic instrument assessed in this chapter consists of the voluntary acceptance, based upon public and private incentives, to deliver a set of pulses or artificial floods designed ad hoc for the partial restoration of the river regime in the Lower Ebro. Since 2003 and with the exception of 2004 and 2005 (dry years) and also 2008 and the spring of 2009 (natural floods), flushing flows have been regularly performed twice a year (at the end of spring and autumn) and have resulted in macrophyte removal rates as high as 95 % in areas close to the dam.