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Muddy floods, i.e. runoff from cultivated areas carrying large quantities of soil, are frequent and widespread in the European loess belt. They are mainly generated in dry zero-order valleys and are nowadays considered as the most likely process transferring material eroded from Cultivated hillslopes during the Holocene to the flood plain. The huge Costs Of Muddy flood damages justify the urgent installation of control measures. In the framework of the 'Soil Erosion Decree' of the Belgian Flemish region, a 12 ha-grassed waterway and three earthen dams have been installed between 2002-2004 in the thalweg of a 300-ha cultivated dry valley in the Belgian loess belt. The measures served their purpose by preventing any Muddy flood in the downstream village, despite the Occurrence of several extreme rainfall events (with a maximum return period of 150 years). The catchment has been intensively monitored from 2005-2007 and 39 runoff events were recorded in that period. Peak discharge (per ha) was reduced by 69% between the upstream and the downstream extremities of the grassed waterway (GWW). Furthermore, runoff was buffered for 5-12 h behind the dams, and the lag time at the outlet of the catchment was thereby increased by 75%. Reinfiltration was also observed within the waterway, runoff coefficients decreasing by a mean of 50% between both extremities of the GWW. Sediment discharge was also reduced by 93% between the GWW's inflow and the Outlet. Before the installation of the control measures, specific sediment yield (SSY) of the catchment reached 3.5 t ha(-1) yr(-1) and an ephemeral gully was observed nearly each year in the catchment. Since the control measures have been installed, no (ephemeral) gully has developed and the SSY of the catchment dropped to a mean of 0.5 t ha(-1) yr(-1). Hence, sediment transfer from the cultivated dry valley to the alluvial plain should dramatically decrease. Total cost of the control measures that are built fora 20 year-period is very low (126 (sic) ha(-1)) compared to the mean damage cost associated with muddy floods in the study area (54 (sic) ha(-1) yr(-1)). Similar measures should therefore be installed to protect other flooded villages of the Belgian loess belt and comparable environments. (C) 2008 Elsevier B.V. All rights reserved.

International audience; Muddy oods due to agricultural runo are a widespread and frequent phenomenon in the European loess belt, and particularly in central Belgium. These oods are triggered when high quantities of runo are generated on cropland and cause severe erosion. Three soil surface characteristics are relevant to determine the runo potential of cultivated soils: soil cover by crops and residues, soil surface crust-ing and roughness. These characteristics have been observed on 65 cultivated elds throughout 2005. A heavy rainfall event representative for events triggering muddy oods in the region (60 mm.h −1 during 30 minutes) has been simulated using a 0.5 m 2 simulator on elds with the 17 most observed combinations of soil surface characteristics in central Belgium. In the case of (ploughed) bare uncrusted soils, runo is not observed, nor in the case of soils covered by crops, showing a transitional crust and a moderate roughness (1-2 cm). In the cases where runo has been observed, mean runo coecients ranged from 13% (wheat in July) to 58% (sugar beet or maize in May and June). Grassed buer strips (GBS) and grassed waterways (GWW) show a higher runo coecient (62% for GBS and 73% for GWW) than most cultivated soils (13-58%). Furthermore, it is demonstrated that small plot measurements can be used to estimate runo generation at the eld scale. A classication of runo generation risk based on the surveys of soil surface characteristics has been applied to common crops of central Belgium. February as well as the period between May and September are the most critical for runo at the eld scale. However, it appears from monitoring of a 16ha-catchment that the highest runoff volumes and peak discharges are recorded between May and August after heavy rainfall, explaining why 85% of muddy floods are recorded during this period in central Belgium.