DETERMINATION OF POWER PROFILE OF HYDRO RESOURCES IN UNGAUGED CHANNELS

The diversification of the Nigeria power generation base requires the exploitation of Nigeria potential hydroelectric power resources which involves the evaluation of the flow characteristics of rivers to determine the hydro power profile and output. This process continues to constitute a daunting challenge in developing countries with poor meteorological and hydrological data base with non-functional gauging channels. The study presents a reliable model for fast, simple and accurate determination of flow characteristics in the hydroelectric power capacity evaluation for rivers and channels in poorly gauged areas and countries like Nigeria. Annual measurements were carried out on River Orle with factors like channel geometry, average monthly velocity and flow rate, and associated potential hydro power determined. The developed model was automated with a Mathcad 14.0 template and validated by comparing its results with the analytical measurement evaluation process of hydropower for different channels. The model output indicates that it has 100% accuracy and precision compared with the analytical process while being faster and user friendly. The results indicate that River Orle has peak power production potentials of 18 MW, base power of 12 MW and low power output of 5 MW. The river is capable of yielding power throughout the year.


Introduction
Adequate power generation is fundamental to industrial development and economic growth of any nation. All vital processes of the economy are driven by electricity in various forms. The standard of living of the people of any country has a direct relation to the degree of electricity availability.
The Nigeria economy has witnessed intractable poor electricity supply challenges for decades which has had far reaching effects on the economy [1]. The reliance on thermal power plants as the major power generation base has not provided the magnitude of sustainable power supply to drive the Nigerian economy [2].
As Nigeria population increases, its economic advancement requires more electricity generation and availability [3]. It is established that in order to diversify the electrical power generation base of Nigeria for improved and sustainable power availability, the assessment and development of potential hydroelectric power sources is an imperative [4], [1]. Nigeria is endowed with several potential hydroelectric power sources that can yield substantial quantity of electricity to power industrial processes in the economy [5].
The main focus of research and development efforts in hydro power generation is currently on the development of small hydro technology because of the low environmental impact [6]. Small hydro power plants has capacity between 1 -15 MW [7].
The exploitation of hydroelectric power generation potentials of hydro sites is done with the evaluation of the flow characteristics of the river channels to determine the profile and maximum power that can be obtained from the site. Some popular methods involve the area -rainfall and area -velocity methods [8]. The area -rainfall method is suitable for territories with reliable and good meteorological data base close to 30 years [9]. The areavelocity method involves the use of the current velocity meter and other related equipments in standard functional gauging stations. The current velocity meter has severe limitations in the measurement of flow data in case of low velocity of flow, shallow depths, excessive velocity, presence of materials in suspension and access problems which are prevalent in developing countries river channels due to the general absence of functional gauging stations [10]. In Edo State in particular there is the complete absence of functional gauging stations along the length of river channels. In such conditions a float is the alternative instrument for measurement [11]. In the absence of functional gauging stations and dire need to improve and complement Nigeria power generation base with hydro technology, there exist the urgency to develop a reliable model to facilitate the accurate and precise assessment of Nigeria hydro power resources for the generation of electricity to sustain the economy.
This study presents a developed model for the fast, accurate, reliable and easy evaluation of the hydroelectric power generation capacity for rivers with poorly gauged channels using floats to overcome the challenges on the proper accurate assessment of the potentials of hydro power resources in ungauged channels. The model will constitute a faster, cheaper and convenient process for the determination of the viability of hydro projects. It will set the course for sustainable power supply to the Nigerian economy by providing a template to facilitate the exploitation of Nigeria hydroelectric power potential with minimal resources. JREAS, Vol. 05, Issue 03, July 2020

Materials and Methods
The study activity involves field experimental studies in the determination of the flow characteristic and hydroelectric power output of River Orle to establish the potential of hydroelectric power that can be obtained from the river. Measurements were carried out for every month of the year for 2018 and 2019 to enable the construction of the hydrograph, flow duration and power duration curve for the river.

Study Area
River Orle originated from Akoko Edo Local Government Area (LGA) of Edo State, Nigeria, runs through Etsako West LGA and discharges into the river Niger at Anegbete in Etsako Central LGA. It has a grid reference of 223000N,182000E [12]. The length of the river is about 100 km [13].The course of the river is located in Edo North of Nigeria. Edo North lies between longitude 6.02 0 -6.69 0 and latitude 6.80 0 -7.11 0 . Rainfall amount in Edo North ranges from 1500mm -2200mm [14].  There are about six to seven months of precipitation in Edo North beginning April/May with cessation in October/November. Over 90% of the rainfall occur between June and October with peak rainfall and run off occurring in September (10).

Development of a Model for Flow Characteristic Measurement
The flow characteristics of a river are evaluated in the Area -Velocity method by measuring the cross section area of a carefully selected channel section and the velocity of flow across the channel. The product of the area and velocity gives the flow rate.

2.2.1Model Development Assumptions
i. The channel flow is steady and turbulent ii.
Continuity of flow holds in the channel iii.
The flow velocity at the ends of the channel is zero iv.
No external flow between inlet and exit of the channel Consider a channel section divided into a number of segments as shown in Fig. 3(a). It is required to determine the velocity in the segments and the average velocity across the channel using the relationship stated as;

=
(1) Imagine the floats to move from section AA' to section BB' covering a distance D in the various segments, in time, ti, ti+1, ------tn respectively. where, n is the number of segments The average velocity in the segments is given as follows segment i is given by Segment n is given by Where, is correction for float velocity Consider a channel section divided into a number of segments as shown in Fig. 2(a).
The average velocity across the channel is given by, = (ℎ 1 + ℎ 2 + ℎ 3 + ℎ 4 + ℎ 5 ) In general term the area of the cross section of a river as indicated in Fig. 2 (b) is given by, The total discharge across the channel is given by, The power output is given by, P = Gross Technical power potentials of the power h = head

Automation of Model
The model was automated with a Mathcad 14.0 template. The inputs data are the segment float time and ordinates. The output are channel area, average velocity, flow rate and hydro power.

Floats Description
The surface float is a ball of synthetic rubber material with weight regulation by air inflation. The double and subsurface floats are made from reinforced paperboard containers. The double float consists of a surface float connected by a string to a subsurface float. The length of the double float depends on the depth of the river.

Stage Setup and Measurement of Flow Characteristics 2.4.1 Selection and Demarcation of Site
The factors that governed the selection of the sites are as follows; i. Straight and uniform cross section and slope, ii.
Well defined ends and beds of channels and stable flow at all stages iii.
Stable flow conditions at the channel sections and it surroundings iv. Sufficient depth for float immersion

Cross-sectional area and depth measurement
Ten vertical points were established across the channel bed to establish the cross sectional profile of the river. Horizontal distance across the river and between the vertical points were measured by direct means using a graduated tape. The depths of the vertical points were measured and an average of the measurement obtained. Each measurement was taken three times.

Stage Set Up
Two types of floats were used in the measurement: Surface float and Double float. The stage setups was guided to minimize random and system errors in dimension taking, length and time of travel of the floats. Large material debris and obstruction were filtered from the length and width of the channels. Shallow depths were avoided or eliminated. Preliminary measurements were made with the floats to observe, identify and minimize system and random errors. The stage was finally marked out after correction for tape sag effects was established according to Eq. (15).

Correction of sag of tape
The correction for Sag of measuring tape is given as; The float velocity was determined by dividing the distance travelled by the float with the time taken to move between the channel cross -sections. The float velocity was taken three times and the average of these measurements was then multiplied by a float velocity correction coefficient ( ) to obtain the mean velocity. The velocity correction factor for the surface and double floats are 0.85 and 0.95. respectively. This velocity was measured for each segment of the divided section of the river.

Head Estimation
Survey instruments were used to determine the elevation of the Orle valley with the consideration that the dam should be situated within the valley. A head of 50 m was established for the the dam.

Hydrographs
The hydrograph shows the variation of river flow rate (m 3 /month) across the year. It consists of the mean monthly flow rate of the river from January to December. The aggregate of the monthly flow rate for 2018 and 2019 for the rivers were used as the monthly mean flow rates to produce the hydrographs of the three rivers. The hydrograph is used in planning the design of the power projects

Flow and Power Duration Curves
The runoff from the rivers were plotted into a flow duration curves which indicates the time the stream flow rate is equaled or exceeded some specified value in the year. The area (arithmetic scale) under the flow duration curve indicates the average yield from the streams. The flow duration curve for the mean monthly flow rate (m 3 /month) was constructed. The power duration curves were constructed by changing the ordinate to the predicted power.
The flow duration curve characterizes the capability of the stream to supply flows of various magnitudes, stream Surface float flow characteristics, type of flood flow regime and the ability of the stream basin to sustain continuous low discharge during the dry season. The exceedence probability of the flow duration curve was calculated using Eq. (16), Where, P is probability of exceedence (%) M is the ranked position of the flow rate n is the number of the measured months

Model Validation
The developed flow rate and power measurement model is configured to measure the area of cross section of the channel, the average velocity, flow rate and gross power output The model was validated by comparing the results with the analytical measurement evaluation process for different channels. The model output indicates that it has 100% accuracy and precision compared with the analytical process. It also automated, faster and simple to apply avoiding tedious calculation process in comparison with the ISO 748: 2007 stipulations.
The validation was done by the use of the model to measure the parameters in the hydroelectric power generation output for channels with different numbers of segments. Fig. 4, indicates the model and analytical method output for the evaluation of the cross sectional area of ten channels.

Presentation and Analysis of Results of Hydroelectric Power Generation Potentials
The developed model was used to evaluate the flow characteristics of River Orle and validated to assess its reliability, precision, accuracy and its ease of application in the power prediction of potential hydro power sites. The model enables the evaluation of the channel geometry of the width and area, flow velocity and flow rate from which the hydroelectric power of the river is derived. With the automation of the model with a Mathcad 14.0 template, the potential hydro power output from any channel can easily be obtained with ease.    Fig. 10 shows the hydrograph of the river which indicates the mean monthly flow rates of the river. From the hydrograph maximum flow yield is obtained in the month of September in the year. The design of the capacity of the dams of the hydropower plants should accommodate this flow regime for the power plant. The dam should be able to accommodate a minimum of 1.763 x 10 8 m 3 of water in the month of September annually as indicated in the hydrographs plot.  Fig. 11 indicates the flow duration curves for the river for the mean monthly flow (m 3 /month). It provides the value of flow that is equal or exceeded monthly for the rivers in a year. The river has a high flow regime which is sustained throughout the month of September with spill over partly to October. This corresponds to Q0 to Q10 on the flow duration curve shown in Fig. 11. In that regime the flow rate of the river is 68.035 m 3 /s with a power output of 33.374 MW at ahead of 50m as indicated in Fig. 12. However, hydropower systems are designed to operate more efficiently between the medium range of flow which is between Q10 to Q70. The medium flow range of River Orle is between 37.852 m 3 /s -12.418 m 3 /s which corresponds to about 18.567 MW -5.266 MW power output, Therefore, river Orle has peak power production potentials of 18 MW, average power of 12 MW and low power of 5 MW.

Statistical Analysis of Data
Statistical analysis of correlation and regression where carried out on the results to determine the level of statistical relationship and control between the results. The regression analysis generated regression model for power prediction using flow rate as the predictor variable. The generated regression equations were validated by using them to evaluate the power output from the experimental discharge results. The Pearson correlation analysis was used to examine the direction and strength of the linear relationship between the experimental and the generated regression model output. The preliminary test for the fulfillment of the assumption of regression gave a Durbin Watson value of 2.441, standardized residuals of -1.293 -+2.072, significance value of 0.000 and with the p -p plots of standardized residuals with dots generally lined up on the 45 0 line, which indicates the fulfillment of all assumption of regression.
The regression plot of power versus flow rate is shown in Fig. 13 and the generated regression equation shown in Eq. (17). The regression analysis indicates a Pearson correlation coefficient of 1, r -square of 1 and r -sqaure (adj) of 1.

Conclusion
The study developed a reliable, simple and fast model compatible with the use of floats in ungauged river channels for the evaluation of gross technical potentials of small hydro power projects with River Orle as a case study. The model validation indicates it has 100% accuracy and precision with the analytical process of hydro power evaluation while being more simple and faster. The model execution is automated with a Mathcad 14.0 template. The study indicates that River Orle has a power production range of 18MW -5 MW annually with average output of 12 MW.