English to French Other Geology

Bonjour,

un géologue explique la fonction d'un "catch basin" :

"In areas where debris flows are frequent, catch basins are one of the few effective solutions. They are built to catch rocks and branches while letting the water pass through. It fills in the basin. At the far end of the basin is a spillway. In the center of the basin there is a stilling well which drains out the water. The ***coarse material*** settles to the bottom of the basin, while the water and the mud continue out the stilling well. If we build a debris basin we can catch the sediment and the water then continues down a channel."

Il doit exister un terme géologique spécifique, mais lequel ?
De plus, on ne peut utiliser "sédiment" qui sera utilisé juste après.

Merci d'avance !