should also be measured, l^enever possible, obtain this information for 

 the time of interest because inlets frequently change shape, especially 

 during major storms. 



Step 2. Construct a flow net (series of cross sections and channels) 

 for the inlet to represent the model grid (Fig, 1). The flow net and 

 inlet discharge are used to determine bottom friction throughout the in- 

 let. The flow net is drawn by approximating the average path (channel) 

 that water follows during ebb flow and floodflow. Channel boundaries 

 are drawn along these paths for up to seven channels. A simple inlet 

 with constant depth and width may be modeled with one or two channels. 

 Complex inlets require approximately three to seven channels. Channels 

 should have the smallest spacing in deep parts of the inlet where flow 

 will be highest. Up to eight cross sections should then be drawn per- 

 pendicular to the channels. The first cross section in the sea and the 

 last cross section in the bay should have cross-sectional areas 10 times 

 larger than the minimum cross-sectional area. Cross sections should be 

 drawn with the narrowest spacing near the minimum cross-sectional area 

 section where friction in the inlet will be high. 



Step 3 . Measure the surface area of the bay at the mean water level, 

 ko, from charts or aerial photos. For most bays the surface area changes 

 as the bay water level rises and falls because sections are flooded at 

 high water levels. If the bay area change is significant, a bay area 

 variation parameter, 3, is used to account for area of the bay, ^hay > 

 at any water level in the bay, h^, using the relation: 



^bay = Ao(l + Sh^) , (2) 



where Aq is the bay surface area at datiom, usually mean low water (MLW) , 

 mean sea level (MSL) , or mean water level (MWL) . 



Step 4 . Specify the seawater level fluctuation as a function of time 

 for the period of interest. Tide tables will give an estimate of the 

 astronomical tide. Water levels can also be measured by a tide gage and 

 stilling well (Seelig, 1977)^. Corps of Engineers and National Oceanic 

 and Atmospheric Administration (NOAA) gages located at niamerous points 

 along the coast may also provide the desired water level information. 

 In this computer program either the tide may be expressed as a sinusoidal 

 wave with a period and amplitude or the levels may be described by instan- 

 taneous sea level measurements at a constant sampling rate. 



Step 5 . Determine the time step of input to the model for use in 

 computations. As a lower limit, the time step. At, should be: 



(3) 



^SEELIG, W.N., "Stilling Well Design for Accurate Water Level Measure- 

 ment," TP 77-2, U.S. Army, Corps of Engineers, Coastal Engineering 

 Research Center, Fort Belvoir, Va. , Jan. 1977. 



