TARRED ROADS AND FISHERIES.
Page 8
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THE committee appointed in May, 1919, jointly by the Road Board (now the Roads Department oh the Ministry of Transport) and the Ministry of Agriculture and Fisheries, to investigate the risk of damage to fisheries by rain washings from tar-treated roads, is not yet in a position to issue a final report upon its investigations, but an experimental station has been set, up at Alresfurd, in Hampshire, and useful experiments have been conducted.
The roadway adjoining the station was recently tarred, and the rain washings therefrom diverted into specially-constructed ponds stocked with fish. It is proposed to continue observations on the tarred road washings throughout the life of the tarred surface, as it is possible 1318 that in its final stages of disintegration the tarred surface may revert to a condition in which it has-greater polluting action on rain washings. Meanwhile, the following, conclusions may be tentatively drawn :— (1 ) Rain washings from a waterbound macadatn road surface are not, in any ordinary circumstances, injurious to fish or fish food.
.(2) The first rain washings from a road surface which has been recently tarred (say, within a week) will certainly be injurious to fish and fish food unless mixed with at least an equal volume of clean water, and may be injurious unless mixed with a considerably larger volume of clean water. They will not, however, be injurious to fish or fish food if diluted with at least 10 times their volume of clean water.
(3) Subsequent rain washings from a tarred road, in the early stages of its life, are not injurious to fish and fish food provided they are mixed with at least an equal volume of clean Water.
(4) Filtration through freshly-cut turf reduces the injurious character of rain washings from a tarred road. '
(5 Storage of rain washings from a tarred road reduces in some respects their toxic character.
(6) There is no evidence that pond vegetation is injured by rain washings from a tarred road.
The foregoing' conclusions apply when the tar used complies with the Road Board specification for tar No. 1.