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~ TRAPEZOIDAL ANO CIRCULAR CHANNEL ANALYSIS HYDROCAIC HYDRAULICS MANUAL. PAGE 15 <br />i <br />j ~ 2.1.2.5 Velocity Head at Normal Depth <br />Water flowing 1n an open channel contains two ma]or types of energy: potential energy and kinetic <br />energy. Potential energy is expressed as the elevation of the water surface. Kinetic energy is <br />' expressed as the 'velocity head". The term "head" can also be stated as "energy level". <br />The velocity head is computed using the following formula: <br />1 <br />VelociryNead = Z <br />8 <br />in which: <br />V =Flow Velocity in the channel (fps) <br />g =Acceleration due to gravity = 32.2 feet/sec/sec <br />2.1.2.6 Energy Head at Normal Depth <br />The "Energy Head" of the flow 1s the total energy of the flow, including both potential energy and <br />kinetic energy. In other words, the energy head is simply the sum of the water surface elevation <br />t and the velocity head. <br />2.1.2.7 Cross-Sectional Area of Flow at Normal Depth <br />The cross-sectional area of flow 1s computed m order to provide a quick check on the other <br />computed quantities. and also to aid in computing excavation requirements for a trapezoidal <br />channel. The flow area of a trapezoidal channel is computed using the following formula: <br />m which: <br />` • A =Cross-sectional Area of Flow (square feet) <br />B =Channel Bottom Width (feet) <br />T =Top Width of Flow (feet) <br />D =Depth of Flow (feGt- <br />The flow area for a circular channel 1s computed by the following formula: <br />A=(F-r)r'-(F-r)r+r'ArcCosl r-Fl <br />r 1J <br />in which: <br />A =Cross-sectional Area of Flow (square feet) <br />F =Depth of Flow (feet) <br />r =Radius of Channel (feet) <br />2.1.2.8 Top Width of Flow at Normal Depth <br />The top width of flow is computed m order to make !t easier to quickly estimate the required <br />right-of--way width for a trapezoidal channel. The top width of the channel will probably be greater <br />than the top width of the flow, because most channels are required to have some freeboard. <br />The top width of flow for a circulaz channel is computed for comparison purposes only. It is <br />computed by the following formula: <br />T =yl-(F-r)r <br />in which: <br />• <br />0 1989 Dodson & Associates, Inc.. 5629 FM 1960 West. State 314, Holston. Texas 77064. (713) 4403787. AU Rlghis Reserved <br />