Water velocity as a control of aquatic snails in concrete canal systems for irrigation

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Water velocity as a control
of aquatic snails in concrete
canal systems for irrigation
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by the/an author.
Additional Information:
• A Doctoral Thesis. Submitted in partial fulfillment of the requirements
for the award of Doctor of Philosophy of Loughborough University.
Metadata Record: https://dspace.lboro.ac.uk/2134/11708
Publisher: (cid:13)c Howard Jones
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WATER VELOCITY
AS A CONTROL OF AQUATIC SNAILS
IN CONCRETE CANAL SYSTEMS FOR
IRRIGATION
By
Howard Jones
A doctoral thesis
Submitted in partial fulfilment of the requirements
for the award of
Doctor of Philosophy
of Loughborough University of Technology
July 1993
© by H R R Jones, 1993
Loughborough University
of Tecl1nology Library
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ABSTRACT
Aquatic snails are the intermediate hosts of the disease schistosomiasis.
Irrigation schemes have often provided a favourable habitat for these
snails, but rapidly flowing water will carry them away.
The research established 23 stations in irrigation canals and monitored
snail numbers and water velocity at these points. A maximum tolerable
velocity for the snail Bulinus truncatus of 0.23 m/s was established,
corresponding to 0.13 m/sat snail height. Aquatic weed did not invalidate
this velocity, but the use of a single control velocity was found to be
over-simplistic. The long-term mean velocity was found to be the best
measure for snail control when velocity varied with time.
Using specially designed filter-traps, snails being carried along by the
flow were intercepted and counted. Attempts to relate these counts to
velocity revealed daily and seasonal cycles of numbers of snails detaching.
Snails in 130 syphon boxes were monitored and the number of snails compared
with water velocity. The maximum velocity tolerated here was lower than in
the canals. Turbulence theory was examined to explain the difference.
The fieldwork was largely carried out in the Tessaout Amont Irrigation
Scheme in Morocco.
Recommendations are made for the design, operation and maintenance of
irrigation schemes, if velocity is to be considered as a snail control.
III
ACKNOWLEDGEMENTS
The control of schistosomiasis is a problem addressed by workers from many
disciplines. It has been an enriching experience while working on this
project to meet and talk with with biologists, parasitologists, doctors,
geographers, mathematicians and human scientists, who have been willing to
share their knowledge with an engineer. The debt owed to all these people
is enormous, but some deserve particular mention here for their helpfulness
and for the relevence and importance of their contribution.
My warm thanks go to the Moroccan government, The Ministries of the
Interior and of Foreign Affairs and all others who gave their permission
for this project to proceed.
The director and staff of the local agricultural and irrigation authority,
the 0. R.M. V. A. Haouz, were tireless in their supply of information. My
particular thanks go to Messrs. Ouzine and Matjinouche in Marrakech, and
Messrs. Saghir, Hanafi and Foughali at the El Attaouia Regional Office.
At the Ministry of Health in Rabat, Morocco, valuable insights were gained
from Dr. Bennouna and Messrs. Azizi, Chakkor and Jad. Mr. Touzara of the
Regional Health Authority at El Kelaa Es-Sraghna gave valuable information
about the local campaigns against schistosomiasis, with Mr. Slimani of the
El Attaouia Health Centre giving day to day details and statistics of the
work. The doctors of this Health Centre, the late Dr. Chaib, and Drs.
Tmara and Khadraoui, all found time to explain the health situation of the
area in their charge with clarity and friendliness in the midst of their
busy schedules.
University links in Morocco were established through the Institut
Agronomique et Veterinaire Hassan II in Rabat. Mme. Chiche, Dr.
Khalaayoune and Messrs. Ait Kadi and Debbargh all gave of their time and
knowledge willingly.
Warm thanks also go to Mr. Akka of the Province d'El Kelaa Es-Sraghna, for
his advice and encouragement.
IV
To the people of the Tessaout Amont area, I owe special thanks. Their
acceptance and warmth to a foreigner whose work they did not understand was
remarkable. I remember the day my watch broke down and I had to time a
five minute trapping test. The only solution was to play a five minute
track from a cassette on the car tape player. How could the locals
understand a researcher who hunts in the canals for snails you cannot eat,
and then plays Mozart to them?
I also pass on my warm thanks to my friends of the expatriate community in
Marrakech. Dr. W. Dougherty of the University of Pennsylvania was a
constant source of encouragement and American insight.
Discussions were held with various workers in the U.K. during the course of
the project. Special thanks must go to Drs. J. Jewsbury and M. Birley of
the Liverpool School of Tropical Medecine, to Dr. D. Brown of the Natural
History Museum, London for identifying snail samples, to Dr. P Bolton of
Hydraulics Research, Wallingford and to Mr. R Carter of Silsoe College, for
arranging and helping with flume tests.
At the University of Loughborough, my thanks go to Dr. P Armstrong of the
Mathematics Department and Dr. P.M. Wade of the Geography Department for
discussions about aquatic weeds. Mr. R. Shaw helped with the production of
some of the drawings. To my two Directors of Research, Prof. J. Pickford
and later Dr. R. Neale, I express my warm thanks and appreciation. My two
supervisors, who have given so much to this project deserve special thanks:
Dr. M. Ince who kindled my interest in engineering for health and has
supported that interest so ably, and Mr I. Smout who has been tireless in
his help and advice.
The financial support for this project from the Science and Engineering
Research Council is gratefully acknowledged.
To my wife, Janet, and two daughters Eleanor and Heather, my thanks could
never be sufficient. You mean more to me than I can say.
V
GLOSSARY
O.R.M.V.A.H. Office Regional de Mise en Valeur Agricole du Haouz, the
agricultural and irrigation authority for the Tessaout
Amont area.
I.A.V. Hassan II The Insti tut Agronomique et Veterinaire Hassan I I in
Rabat.
VI