The effects of drainage on the flora and fauna of a tributary of the River Boyne

Arterial drainage helps in the process of land reclamation by lowering the level of the existing river bed and allowing the ground water to run off more quickly. In recent years the Rivers Corrib, Dee-Glyde, and Moy have been drained. The effects of drainage on the fish stocks and the invertebrate fauna of the River Moy have been described by Toner, 0'Riordan and Twomey (1965). In 1968 investigations commenced into the effects of drainage on the invertebrate fauna and flora as well as fish stocks in the Trimblestown, or Athboy, River, a tributary of the River Boyne. The Boyne rises 6.4 km from Edenderry and flows north-east for 112 km to the sea at Drogheda. It has fifteen tributary streams and two lakes in its catchment area of 2,693 square km. A section of the Trimblestovn River which rises at the foot of Slieve na Calligh, Co Westmesth and flows south-east for 35 km to meet the Boyne at the town of Trim was selected. Its shallowness and accessibility made it particularly suitable for the study. The study area 4.8km north of Athboy town, was 146 metres long and averaged 6.1 metres wide. The river flows for its entire length over Carboniferous limestone end the bed of the river consists of gavel and sandy silt, with scattered boulders and some mud in the quieter areas. There are a few pools in this section, the river being composed of riffle areas alternating with flats. The normal flow at this point was 0.77 cubic metres per second, the pH was 7.6 and the alkalinity as CaCo3 was 310 p.p.m. From 1968 and 1970, 57 invertebrate fauna samples from standard areas (0.093 sq.m) were taken with a suber stream bottom sampler. The plant life was mapped and an assessment of the fish population was made, by the depletion method