He rereke te tapahi o te awa Ko te tikanga o te pakitara hohonu (TRD mo te poto) he rereke ki te tikanga o te Taiepa Whakaranu Whenua (SMW). Ma te tikanga TRD, ka whakairihia nga taputapu kani ki runga i te waahanga tapawha roa "pou tapahi" ka whakauruhia ki roto i te whenua, kia nekehia kia whakawhiti mo te tapahi me te ringihanga grout, te whakaranu, te whakaoho, me te whakakotahi i te oneone i te waahi tuatahi, kia pai ai hanga he pakitara diaphragm i raro i te whenua.