Laserfiche WebLink
<br />METHODS AVAILABLE IN HEC-2 <br /> <br />The program computes the energy loss caused by structures such as <br /> <br /> <br />bridges and culverts in two parts. One part consists of the losses <br /> <br /> <br />that occur in reaches immediately upstream and downstream from the bridge <br /> <br /> <br />where contraction and expansion of the flow is taking place. The second <br /> <br /> <br />part consists of losses at the structure itself. As an alternative to <br /> <br /> <br />having the program compute the losses. it is possible to input a loss <br /> <br /> <br />(or water surface elevation) determined externally from the program. <br /> <br />Contraction & Expansion Losses <br /> <br />Losses due to contraction and expansion of flow between cross sec- <br />tions are determined by standard step profile calculations. Manning's <br />equation is used to calculate friction losses. and all other losses are <br />described in terms of a coefficient times the absolute value of the change <br />in velocity head between adjacent cross sections. When the velocity head <br />increases in the downstream direction. a contraction coefficient is used; <br />and when the velocity head decreases. an expansion coefficient is used. <br />The second part of the loss calculation. for losses that occur <br />at the structure itself. is made by either the normal bridge routine <br />or the special bridge routine. <br /> <br />Normal Bridge Routine <br /> <br />The normal bridge routine handles a bridge cross section in the <br />same manner as a natural river cross section. except that the area of the <br /> <br />2 <br />