Effects of agricultural drainage on streamflow

Robinson, M. (Mark), 1953-

May 1990

Thesis or dissertation

© 1990 1953- M (Mark) Robinson. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.

There is a long-standing controversy regarding the effects of agricultural drainage on streamflow. This debate has continued, unresolved, largely due to the lack of factual data.

This thesis assembles and analyses a far more comprehensive set of field data than has previously been studied. It shows that, in general, field drainage reduces peak flows from clay soils and increases them from more permeable soil types. The critical role of the pre-drained soil water regime is examined and guidelines presented enabling the likely effect of drainage on field outflows to be predicted from measurable site parameters. These findings are supported by the results of computer simulation modelling, which also enables the effect of drainage under different rainfall regimes to be studied.

As larger areas are considered, the importance of outfall channel improvements becomes dominant. They increase in-channel flow velocities and reduce overbank flooding and storage, and may result in higher maximum river flows even in an area where drainage reduces peak flows at the field scale. The impact of arterial channel improvements is greater for larger floods and for channels with bigger design flow capacities.

In a regional study of some 80 catchments it was found that those with more extensive drainage tended to have shorter rainfall to runoff response times; however, no effect was discernible on flood frequency.

Department of Geography, The University of Hull
Sponsor (Organisation)
Great Britain. Ministry of Agriculture, Fisheries and Food; Natural Environment Research Council (Great Britain)
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