Flush systems for dairy manure removal: the alley roughness value

ABSTRACT The note proposes an hydraulic approach to the flush system for removing manure from alleys in dairy freestall barns. The flushing flux is able to transport manure along the alley flooring, depending on hydraulic flux parameters. Chezy formula has been commonly used to calculate the mean flow velocity, assigning a constant value to the roughness Manning coefficient. Attention is posed on the variability of that coefficient, depending on both the flooring material and the type and quantity of material lying on the floor. Trials in three barns, located nearby Reggio Emilia in the North of Italy, which have been using the flushing system for some years, have been performed to calculate the Manning coefficient n values once it was known the flow flush velocity. The obtained n value for the clean alley, concrete floored with grooves, differently increases depending on the alley use, feeding or freestall, because of the type and quantity of bedding materials present only in the freestall alley. N-values close to 0.02, as suggested in literature, are found only for the freestall alleys. As a consequence of using a constant roughness value for both the alleys, the flow velocity results under estimated in the feeding alley and over estimated in the freestall one.