Abstract
This research examines the consistency of the value of tidal datum obtained for Nwaniba River in Akwa Ibom State of the Niger Delta (Nigeria). Two sets of tidal data from 10/05/2007-10/06/2007 and 10/05/2017-10/06/2017 observed three (3) times a day (Morning: 7:30-9:30; afternoon: 12:00-14:00 and evening: 16: 00-18: 00) at every 2 minutes interval using manual tide gauge were considered in order to evaluate a trend. Mean Highest Water Level (MHWL), Mean Lowest Water Level (MLWL) and Mean Water Level (MWL) for the 3 times per day were computed. The weekly and average MHWL and MLWL for the period were also computed. The results show that the water level measured within (10/05/2017-10/06/2017) is higher than that of (10/05/2007-10/06/2007) except in few cases. The highest (149.000cm) water levels for 2007 observations were recorded on 08/06/2007 at (08:40am) and on 10/05/2007 at (7:46am) while the lowest level (1.80cm) was observed on the 23/05/2007 at (8:28am). For 2017 observations, the highest (152.300cm) water levels were recorded on the 15/05/2017 at (07:53am) and on the 27/05/2017 at (9: 08am). The lowest water level (1.801cm) was recorded on the 08/06/2017 at (08:32am). In 2007, the observed Lowest Water Level (LWL) of1.800cm was adopted as the tidal datum for the River but in 2017 the LWL obtained is 1.801cm. The difference between LWL for 2017 and 2007 which is defined as (δLW) is 0.001cm. The value of (δLWL) = 0.001 cm shows that the value of LWL of 1.800cm adopted in 2007 as the tidal datum still remains consistent when compared to the observed LWL of 1.801cm for 2017 observations. Based on the LWL obtained for 2007 and 2017, it can be concluded that the tidal datum for Nwaniba River is consistent from 2007 to 2017. Also, based on the difference between average MWL for 2007 and 2017 = (δMWL) = 1.247cm, it can be concluded that the water level at Nwaniba River has increased with 1.247cm for the period of observations. In addition, the range of values of R2 obtained is 0.000-0.046 i.e. 5%, which shows that only 5% of the variation in MHWL and MLWL can only be attributed to the variation in time.

Key words: Tidal datum, Mean Highest Water Level (MHWL), Mean Lowest Water Level (MLWL), Mean Water Level (MWL), Nwaniba River, Niger Delta