Mattituck Creek Water Level

Figure 6-4. Mattituck Creek water-level measurements and calculations by CEA

model

Ocean tide amplitude (ft)

3.0

Channel length (ft)

3,000

6

Bay surface area (sq ft)

7.2 x 10

Channel width (ft)

200

Hydraulic radius (ft)

9.3

Channel area (sq ft)

1,600

The calibrated CEA model produced the stability curve shown in Figure 6-5,

giving a predicted stable equilibrium area of 1,020 ft for Mattituck Inlet. In an

Escoffier inlet stability analysis, if the calculated velocity for the inlet falls below

the equilibrium velocity (or is tangent to it at a single point), the inlet is unstable

and will close. If the two curves intersect at two points (as for Mattituck Inlet),

the point on the right is identified as the stable equilibrium cross-sectional area.

If the channel area is larger than this, the tidal current velocity in the inlet will

decrease, promoting channel infilling and a return to the stable condition. If the

channel area decreases, the tidal current velocity in the inlet will increase,

scouring the channel until it returns to stable cross-sectional area. The

intersection on the left side of the Escoffier curve denotes an unstable condition.

If the channel area decreases beyond this point, velocity will decrease and the

inlet will tend toward closure because friction will reduce the velocity further.

274

Chapter 6 Inlet Morphology and Stability

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