**8. Tidal hydrology**

The daily tide data in Escravos for one annual cycle (2004) comprising about 1400 specific tide measurements (four readings per day for 1 year) were used to characterize the tidal hydrology of the area. The separation of tide phases into neap and spring tides was with regards to the moon phases.

Highlights of the tidal hydrology of the area based on tide measurements at Escravos bar (the closest tide station to the area which is about 10 km east of Awoye is presented in **Table 3**. The highest (or extreme) high water individual spring tide

*Climate Change and Anthropogenic Impacts on the Ecosystem of the Transgressive Mud Coastal… DOI: http://dx.doi.org/10.5772/intechopen.105760*


#### **Table 3.**

*Summary of the Tidal Hydrology of the region.*

(EHWS) recorded over the one-year period was 1.77 m, and it was recorded 17th of April of the study year, a day after the full moon i.e. during the spring tide when the sun was passing the equator.

Mean high water of springs (MHWS) and mean low water of springs (MLWS) were 1.50 ± 0.12 m and 0.44 ± 0.17 m respectively, thus giving a mean range of spring tides values of 1.06 m (which is about 90% of the observed extreme range of springs tide). On the other hand, the mean high-water level of neap tides (MHWN) and low water level of neap tides (MLWN) were 1.37 ± 0.15 m and 0.57 ± 0.16 m, respectively. Giving a mean range of neap tides values of 0.8 m, which is about 55% of the observed extreme range of spring tides and about 80% of mean range of spring tides. Average high tide level (AHTL) and average low tide level (ALTL) were 1.44 ± 0.15 m and 0.51 ± 0.18 m respectively, while midtide level (MTL) for all recorded tides (n = 1409) was 0.97 ± 0.49 m (**Table 3** and **Figure 3**). The mean range of spring tides could be divided broadly into three commonly observed shore zones: the upper shore zone (the portion above the mean range of neap tides), the middle shore zone (corresponding to the mean range of neap tides), and the lower shore zone (corresponding to the portion below the mean range of neap tides). Two harmonic tide waves influence the tidal variation along the coastline of the area, one with a period of 12.5 hours and the other with a period of 25 hours [20]. The combination of these two harmonic tide waves usually produces two low tides and two high tides each day. The twice-daily (semidiurnal) tide of 12.5 hours predominates over the daily (diurnal) tide of 25 hours, generating a diurnal inequality, or mixed semidiurnal tides. This causes a difference in height between successive high and low waters. The result is two high waters and two low waters each day [21]. The tidal characteristics of the area have many features in common with those of the typical Atlantic coast with the domination of two unequal high water and two low waters occurring within 24 hours [22]. The mean neap range of 0.49 m recorded in the area is comparable with the British coasts amounting to between 0.45 and 0.55 m of the mean spring range [22]. This small neap range is typical of locations where tidal ranges are large. However, the overall mean range of about 1.1 m (MHWS-MLWS) in this area is lower than 1.7 m for Bonny bar and 2.0 m for Calabar in Nigeria.

**Figure 3.** *Variations of the Tidal Hydrology of study region.*

## **9. Relief and drainage**

The area falls within the Atlantic system where most of the rivers are short, northsouth flowing coastal rivers which follow more or less regular courses [23] and which drain into the sea. Rivers are being divided in a fairly simple line by western plains and ridges. The two major rivers, River Oluwa and River Ominla, display a drainage pattern which is dendritic but each river is parallel to the other and having a different tributaries. In the coastal plain area, river valley gradient is very low as it discharges its loads, leading to braided channel formation. Awoye and Abereke estuaries are the two major estuaries in the region. Abereke estuary located in the northern part of the area receives drainage from the Oluwa River and other major surrounding creeks. On the other hand, Awoye estuary located in the southernmost part of the area receives drainage from Ominla River, surrounding creeks and Benin River from Delta State.

## **10. Economic characteristics**

The economy of the region is centred mainly on fishing, lumbering, farming, palm wine tapping, mat-weaving and petty trading. Fishing is the economic mainstay of

*Climate Change and Anthropogenic Impacts on the Ecosystem of the Transgressive Mud Coastal… DOI: http://dx.doi.org/10.5772/intechopen.105760*

the people in the region. The economic activities and the resultant occupation of the people have traditionally been related to the natural environment. This provides an opportunity for people in the riverine to be involved primarily in fishing, while people in the upland areas combine both farming and fishing with lumbering and carving of boats among other activities. A considerable number of people engage in traditional craft and modern processing industries. About 80% of the people in the area engage in fishing and that creates employment and generates a substantial income of about 90% of local GDP. Fishing activities in the area are carried out in two ways—freshwater fishing and ocean fishing.
