Water Exchange and Channel Friction Related to Tidal Flow in Tudor Creek System, Kenya Coast, Western Indian Ocean.

Abstract

The Tudor creek syr,tem, located in mid-Kenya coast is formed by a sinuous channel,Tudor channel, between Mombasa port and Tudor harbour, which connects the inner wide and shallow basin,the Tudor creek, to Kilindini harbour and the Western Indian Ocean. Two seasonal rivers,Kombeni and Tsivu enter it. The creek is surrounded by mangrove wetlands,while it's off-shore area is shielded by shore-parallel reefs on both sides of the entrance. We have studied the tidal flow in the channel by RCMs and the tidal heights within the creek and outside with tide gauges obtaining the following results.The tide is semidiurnal with a form number of 0.18. The neap and spring tidal range is 1.7 m and 3.1 m in the creek. The flood tide lasts 6.5h while ebb tide extends for 6.3h. Mean flood and ebb currents are 0.36 ms-1 and 0.40 ms-1respectively. There is a marginal phase lag between the entrance and the creek. A high evaporation compared to fresh-water input during peak dry period, influence the salinities. During this season the creek is well mixed with lower salinity water on the oceanic side and high salinity water in the creek. The average volume flux due to the tide is 2600m3s·1 but the net exchange of water related to the residence time is 60 m3s·1. The residence time as determined from the NE monsoon peak dry season is of the order of two weeks.The bottom layer parameters; friction velocity, roughness length and drag coefficient have been estimated from pendelum current measurements assuming a logarithmic profile. Average values were 0.04 m s·1, 0.34 m, and 8.3 x 10.3 respectively. Heat flux and radiation balance is studied on the basis of temperature measurements.