Factors Affecting Hydrodynamics of a Lake Essay

Introduction

Amongst all other natural resources available to mankind, lakes are of immense value, holding importance as the water supply for many. Lakes provide water for food, irrigation and farming, transportation and commuting, recreation, and hydropower. A large amount of flora and fauna additionally survives with this form of natural water supply.

Approximately 1.7% of the Earth’s surface is covered with lakes, which amount to a total area of 2.3 × 10⁶ km². More than 110,000 lakes exist, which are larger than 1 km². Millions of small lakes are also present, of which 800,000 are artificial reservoirs, created over an area of 0.5 × 10⁶ km² (0.2 × 10⁶ mi²). There are many dependents on these lakes, especially residents of cities who do not reside near the coast. These people tend to rely on natural resources for their living, lakes being one of them, as water is a basic commodity. However, the development that is being undertaken near or alongside lakes has caused and is continuously water pollution due to nutrients being released into the freshwater supplies. Pollutants pose a threat to the aquatic organisms present in the lakes, whereas the nutrients cause harm due to heavy algae growth (McGinnis, 2008).

Factors Affecting Hydrodynamics of a Lake

Soil moisture

Soil moisture is determined by the movement of dissolved solutes and their rapidity pattern. They are moved from one place to another by the streamflow, and the rates of these movements vary. A spreading action is caused which is dependent on the way the flow is carried out.

The dispersion (σ_D) caused in a one-direction flow is relative to the square root of linear liquid displacement. This proportionality constant is an important feature of the system of flow of water and can be found out with experiments. It is seen that the dispersion sum attained from a given amount of linear displacement is theoretically free of the flowing speed, not being dependent on it. Furthermore, Scheidegger’s probability theory indicates that the movement of the dissolved solutes in soil moisture cannot be taken from the average water flow speed until the hydrodynamic dispersion effect is considered (Day and Forsythe, 1957).

Some soil moisture results obtained show the following results, with moisture being more near the riverside path.

• Soil Moisture

Group Easting Northing Soil Moisture (%) Comments

C 73833 71877 44.1

73824 71873 50.0

73814 71869 48.0

73806 71868 38.4

73795 71867 50.6 near the riverside path

73782 71864 60.7

73771 71860 52.8

The soil that is under grassed terraces is found to be wetter than those under forested terraces, with indications of variability in hydrodynamic response. The hydrodynamic behavior of the soil particles caused by the retention curves shows high water content in potential ranges. High values are observed during dry periods and a lower value of saturated hydraulic conductivity is seen in wet periods (Hydrodynamics).

Flow in the Culverts

The stratification season changes the flow of the waters. There is no longer any vertical movement; the waters tend to take a horizontal change whilst following contours of equal density. This horizontal movement is caused by two factors, which are, the wind, and density differences prevalent. Water is proved to be 800 times denser than air. With the provision of momentum to the surface of the water, lakes receive only near 3.5% wind energy from the environment. Some of this energy is dispersed by the waves of the surface, and the rest is converted to large-scale currents. These currents amount to 1.5-3% of the speed of the wind.

The larger lakes have a unique water flow method. When the wind stops blowing, the water displacement changes from the upward and downward movement to two-layer movements, which oscillate in opposite directions. This gives rise to a vertical alteration of temperature isotherms. Mostly these two-layer patterns are observed in lakes, but at times, three layered motions are also visible, with the top and bottom layers moving in one direction and the thermocline present in between, in the opposite direction. This ‘seiching’ effect is present for many days in small lakes, and months in large lakes. It stops due to the energy being diminished after friction takes its course (Lake hydrodynamics).

In lakes and rivers, turbulence is shown to be present in two layers, the top, and the bottom. The bottom layer proves to be perfect in terms of being a logarithmic layer, and the changes of large-scale motions to turbulence occur here mostly (Alfred Wüest and Andreas Lorke, 2003).

Pipes

The theory applicable to hydrodynamics is difficult to attain in open waters such as rivers and lakes, due to the many factors that affect water flow. Hydrodynamic issues can be addressed only by analysis through man-made engineered channels, such as pipes.

When movement between a fluid like water and the container is taking place, it produces water flow. The flow of any liquid through a pipe is dependent also on its viscosity, or the ability to stick to the surface. The elements of the liquid that are nearest to the boundaries of the container cause a slow down in motion. The velocity is greatest at the parts where the fluid is most distant from the walls of the pipe. All of these elements are dependent upon the velocity of the liquid and the container in which it is present (Hydraulics).

Pipes and the liquid that flows through them are interdependent, in that the larger pipes the flow rate of water will prove to be higher than in smaller pipes. The diameter of the pipes is dependent as well as the inner area, on the turbulence obtained. If the flow rate obtained is 12cm/s, it shows that the size of the pipe is small and is not producing a high flow of water.

Flow in pipes river

The radius of pipe R cm 100

Max depth d cm 200

Angle AOB radians 6.283185

Sector Area cm^2 31415.93

Triangle area cm^2 -1.2E-12

Water Area cm^2 31415.93

Flowrate cm/s 12

Dilution Gauging

The measurement of streamflow can be made through dilution gauging, with the rate of dispersal of a tracer, with its concentration when examined downstream. This method is applicable in streams and lakes with very high turbulence, and heavy flows, where it is complicated to apply the conventional methods of stream velocity measurements. The tracers are chemical ones, such as salt, (NaCl), and can be examined with an electrical conductivity (EC) meter, or an ion electrode of a certain specification. If a fluorescent dye is used, like Rhodamine WT, a fluorometer can be used for its monitoring. The samples of water can be collected at varying instances to be taken for laboratory study (Dilution Stream flow Gauging).

The use of the tracer is also known as the slug injection method. The tracer concentration and measurement time are seen at a downstream area, before, and after the introduction of the slug. The slug can also be inserted at a constant rate, varying the process, and is called the constant injection method.

The salt insertion method is also called the gulp injection technique. It is commonly used. Results show that the introduction of salts into the water increases the streamflow. During low and medium movements, the flow increased substantially, but not during high flows. This may be because of the natural link between the fast movements and flows (Wood and Dykes, 2002).

Conclusion

The drift of streams is dependant on the particles that are present in the streams, along with the slope steepness and height of waves. The moisture levels obtained in the soil are dependent on the flow of streams and lakes, with more moisture at the ends of where heavy flowing lakes run. The wind flow and density affect the waves being formed. The density affects the movements that take place in the water. The pipes through which water flow is measured additionally affect the flow of water.

The techniques used in the measurement of stream flows include the salt insertion method, which has better credibility in obtaining accurate results. This is the best-suited method, with the lowest ecological impacts upon usage (Butterworth et al, 2007). The alternate methods of dilution gauging cause effects on the ecological environment, causing harm to the environment.

References List

1. Alfred Wüest and Andreas Lorke (2003). SMALL-SCALE HYDRODYNAMICS IN LAKES. Annual Review of Fluid Mechanics, Vol. 35: 373-412 (Volume publication date 2003). Applied Aquatic Ecology (APEC), Limnological Research Center, EAWAG, Kastanienbaum, Switzerland;
2. B. Shteinman¹ , Y. Kamenir and M. Gophen (1999). Effect of hydrodynamic factors on benthic communities in Lake Kinneret. Hydrobiologia. Volume 408-409, Number 0, 1999
3. Dilution Stream flow Gauging.
4. Hydraulics. Web.
5. Hydrodynamics.
6. J. A. Butterworth, E. J. Hewitt, M. P. McCartney, Senior Scientist, Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent, UK Discharge Measurement Using Portable Dilution Gauging Flowmeters. Hydrologists, Institute of Hydrology, Wallingford, Oxfordshire, UK. Water and Environment Journal. Volume 14 Issue 6, Pages 436 – 441.
7. Lake Hydrodynamics.
8. McGinnis, D (2008). Lake hydrodynamics. McGraw-Hill’s Access Science. Encyclopedia of Science and technology online.
9. P. J. Wood^, and A. P. Dykes (2002). The use of salt dilution gauging techniques: ecological considerations and insights. Water Research. Volume 36, Issue 12, 2002, Pages 3054-3062
10. Paul R. Day and Warren M. Forsythe (1957). Hydrodynamic Dispersion of Solutes in the Soil Moisture Stream. Published in Soil Sci Soc Am J 21:477-480 (1957). © 1957 Soil Science Society of America, 677 S. Segoe Rd., Madison, WI 53711 USA