EROSION PATTERN BELOW A CONCRETE APRON BY FLOW FROM A TAILRACE TUNNEL

The analysis erosion occurrence below a concrete apron by flow from a tailrace tunnel is
presented. The outcome from the analysis was used to determine the appropriate
arrangement and sizes of baft1e blocks to protect the bed material of the physical model
from being eroded by the flow. The project was started with literature review on the basic
concept of dam, sediment transport, properties of sediment, armoring and hydraulic jump.
Study on erosion pattern which was conducted by other professional is also highlighted in
the literature review. The study on analyzing scour occurrence has been conducted to
explain the similarity existing in the scour process and profile including dune in the
downstream of the scour hole. Altogether, twelve experiments to study the erosion profile
have been carried out using six types of baft1e block arrangements including two
experiments without using the baft1e blocks. The experiments took place at Pergau Pond
Model in UTP lab. Sieve analysis test was conducted prior to the beginning of the
experiment to determine the size of sediments that were used throughout the project.
Sediments size used in the project range from 300J.!m to 350J.!m. Two discharges used in
the project were 121/s and 301/s. The purpose of choosing the discharge are to ensure
that the constant parameter being used. The reason being is also to observe the severity of
the erosion occurrence if the discharge is too small and also if it is too large. It took one
hour to complete each test. The pictures of scour pattern were taken as materials to be
analyzed. Also, the patterns were drawn to scale whereby a plastic cover was spread onto
the sediments. The maximum distance of scour dispersion from the apron were measured.
Five lines of measurements were selected to measure the scour profile downstream the
apron. The result indicated that the most severe erosion occurred at the downstream of
the incoming flow from the tailrace tunnel. From the observation and comparison of
maximum scour depth, the findings proved that Set 4 is the most efficient energy
dissipater.