Engineering Hydrology - Essay Example

?RIVER FLOW ANALYSIS Introduction The requirement of this paper is to provide a feasibility phase for tinning factory. Theproposed development site for this factory borders the flood plain of Boyd River. The new site will be able to displace the flood region of River Boyd which is located at Bitton as well as to displace the course of the river flow. To achieve all these development plans, a careful flood risk assessment should be conducted. This would ensure that the new factory site for tinning factory will not be affected by floods that might arise from Boyd River. Minimization of surface run off is also required by Environment Agency. This is because if the runoff is not minimized then a lot of destruction will be done to the environment. As a consulting engineering hydrologist, my task will include carrying out preliminary assessment before authorization of the development plans. The preliminary assessment will include water resource assessment, drainage assessment, and flood risk assessment. All these preliminary assessments require critical flow analysis of Boyd River so as to ascertain the strength of the river flow (Black, 1996). Methodology The data for the flow analysis of Boyd River will be obtained from the official website of the Environmental Agency. This site will be able to provide a recent map of Boyd River as well as other essential data regarding the river. Apart from this, more data will be obtained from the actual Boyd River site. This would act as a primary data and the collection instruments to be used will be stream gauges. These gauges are able to provide accurate data since they are able to measure the amount of water that flows in an open channel. The current meter is one of such gauges that will be used. This gauge is accurate because it combines both river velocity as well as the angular velocity of the rotor on the meter. From the already gathered information about the River Boyd details such as width, depth, and the sloping gradient the best meter to be used will be vertical axis current meter. This current meter can either be Price Type AA or pygmy model (Hauer & Gary, 2007). Methods for river flow analysis The successful development of tinning factory requires proper understanding of the flow analysis of River Boyd. As a consulting engineering hydrologist, the information that is necessary in the successful implementation of this development plan is the information concerning the nature of the River Boyd. Rivers are classified as either perennial, ephemeral, and intermittent. All these classifications are brought about by base flow or storm flow and river discharge. The various methods used for river flow analysis depends on the relative frequency, duration of certain river levels, and duration of low and high flows. The discharge (Q) or stream flow of the river is the amount of water flowing in the river. More precisely, these terms are used for the volume of water that flows through a given point of the river and they combine storm flow and base flow. The points along the cross-sectional flow area and the water velocity are referred to as measurement point for discharge or stream flow. Some of the methods which are used in determination of river flow analysis are (Hauer & Gary, 2007); Floating objects methods This method takes into consideration the time taken by a floating object to cover a certain distance. All the measurements for the cross-sectional flow of the river should be done simultaneously. The formula to be used here is Q = VA where Q is discharge (m3/sec), V is river velocity (m/sec), and A is the cross-sectional area of the river (m2). The limitation of this method is that it is not accurate more so for very wide rivers such as River Boyd with approximate width of 11 m. This is because the velocity of the river keeps on varying from one point to another due to depth and cross-sectional area of the stream. Stream gauging method In this method, the cross-sectional area of the river is subdivided into proportional vertical sections. The velocity profile is then measured according to each vertical section. The mean velocity is obtained for each vertical section using the flow meter. The area of each vertical section is then obtained and the computation of the mean discharge is done using the following formula; Q = ? VA The accuracy of the measurement can be enhanced by having numerous vertical subsections. Developing rating curve method This method applies rating curves from stream gauging instruments. The curves are obtained at different seasons and flows of the river. Buoyant balls are incorporated in floating gauges. These balls are able to rise and fall. These rising and falling sequences cause an increase and decrease in water level respectively. Pressure transducers are then installed below these gauges so as to record the increasing pressure caused by rising and falling of water levels. The data from these pressure transducers are then transferred to data loggers which are situated at the banks of the river (Hauer & Gary, 2007). Precalibrated structures methods This method is applicable in small rivers. These structures are used because they are accurate and convenient. Some of the structures are weirs and flumes. Weirs These structures are built in the river and they force the river water to flow through an opening called shape or size. Notch control and stream gauging stations form weir structures. The flow of the water must be directed through the notch otherwise accurate results will not be obtained. Flumes These are artificial channels which are constructed so as to maintain water flow through certain designed cross-sections and lengths. Stilling well is used to measure water height in flumes. This height measurement is essential when calculating discharge. Examples of flumes are Parshall flumes, HS, H, HL, and Venturi type. All the H types of flumes are used for measuring intermittent surface run off. Venturi type is meant for measuring irrigation water, while San Dimas type is used for measuring debris –laden river flow more so in Mountain Rivers (Hauer & Gary, 2007). Results Description of the results The POT threshold of River Boyd is given as 5.88m3/s. This is the pressure of point as recorded in the pressure transducers. This value is relatively high and therefore, all the premises such as tinning factory foot print and car park should be constructed at a slope less than one. The maximum velocity of the river is given as 11.59m3/s and its area of coverage as 47.71km2. From the area of coverage, it can be said that the flood plains for River Boyd is relatively large. This means that for the tinning factory project to be successful, the channel slope should be raised above 0.005 (Grant & Gary, 1997). Discussions and Analysis Q = 11.59m3/s, A = 11*4 = 44 m2 Q = VA 11.59 = V*44 V= 11.59/44 = 0.2634m/s Area of River Boyd From the flow analysis data, the flooding area of the river is given as 47.71 km2. Total area of the site = 2.86 ha If 1ha. = 10, 000m2 2.86ha. = 2.86*10, 000 = 28,600m2 The area covered by the flood plain is relatively large therefore, the sloping of 1 % towards the river should be increase so as to ensure that the water from the river do not flood the tinning factory premises. The foot print of the factory should be raised by close to 0.005 The type of weir structure built in River Boyd is Flat V. The weir has 8 m wide crest and the rated sections high flows are situated in rectangular sheet. These sheets are 4 m deep. The recent map for Bitton Station (053017) has location marked in purple color. All the area within the purple shaded area is prone to flooding. The Environmental Agency takes the initiative to warn all the residents of such places of likelihood of occurrence of floods. They are advised to take immediate action in case they receive flood warning (Grant & Brian, 1997). Flood alert areas All the businesses or homes located within the pink areas are often given free flood alerts calls. The flood alerts are always issued when the floods are about to attack. The flooding alerts are due to sea, rivers, and underground water. Local geology constitutes to the underground flooding and therefore, it is very difficult to predict it. River levels Monitoring sensors for the river level are place in the river at key points. River level monitoring is done after every 15 minutes. This information is then sent to Environmental Agency offices for online publication on a daily basis. Recommendations The development site for tinning factory should be critical analyst by geologist. This is because from the Environmental Agency department, underground drainage is determined by the nature of the geology. A lot of information concerning flow analysis River Boyd is not available at Environment Agency department. The little information that they have only considers the river at Bitton Station (053017). Therefore, an extensive research should be done along the river so as available more flow data. Before construction of tinning factory, a number of considerations should be put in place. Some of the considerations are; The gradient of the slope should be raised by 0.005. This will ensure maximum protection against flooding. Extensive research should be done before setting the factory because the flooding area of the river is relatively large. Conclusion River flow analysis is can be best determined through the use of stream gauging method. This is because this method is accurate and convenient. Before setting up tinning factory, the management should ensure that they gather valuable information from Environmental Agency regarding underground drainage. Bibliography Black, P.E. 1996. Watershed Hydrology [2nd Ed.]. Chelsea: Ann Arbor Press, Pp.449 Grant, D.M., & Brian, D.D. 1997. Isco Open Channel Flow Measurement Handbook [5th Ed.]. New York: Lincoln Publishers, Pp. 267 Hauer, F.R., & Gary, A. L. 2007. Methods in Stream Ecology [2nd Ed.]. San Diego: Academic press, Pp. 56 APPENDIX Data presentation for flow analysis POT threshold 5.88 m3/s Bank full stage 4m Height of wing walls 4m Maximum gauge flow 11.59 m3/s Maximum gauge level 0.91 Catchments descriptors Area 47.71km2 SAAR 806 mm BFIHOST 0.497 PROPWET FARL 0.35 0.998 URBEXT 0.0124 Table1. STREAM GAUGE DATA Figure2 PIE CHART FOR FLOW ANALYSIS Figure 3 BAR GRAPH FOR FLOW ANALYSIS Figure 4 Read More