Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
The traditional prayers at Timket for the water blessings are absolutely identical to those chanted at Baptismal services, which are generally also verbatim of the first verses of the Preparatory Prayers of the Divine Liturgy and the Gospel reading the John 3 (Nicodemus)http://www.ethiopianorthodox.org/amharic/yezemametsheft/zematarik/kidasse%20Dioscoros.pdf
(here is a link)
The hymn chanted with choir and drum is the mahalet timket
(Baptismal Praise) which both precedes and concludes the Timket service including the culmination of the Tabot procession. I do not have the words at the moment but I can get some for you from my priest, I would enjoy a copy myself.http://www.ethiopianorthodox.org/amharic/seasonal/timket.html
(this site has some relevant media files, but the writings are all in Amharic)