# Tides

## Tidal boundary condition

This is specified at each open boundary node on all segments that require this type of b.c. The elevations at those nodes are simply sum of all harmonics read in from bctides.in (see below).

## Earth tidal potential

The tidal potential enters the momentum equation as a body force term:

## Input

In SCHISM, tidal b.c. (boundary condition) and earth tidal potential are specified in bctides.in

8 5. ntip !! number of todal potential constituents, cut off depth (m). The latter is used to save a little computational time as tidal potential is negligible in shallow water. To include all depths in calculation, set a negative depth like -100.

M2 !!First frequency name

2 0.242339 1.405189e-04 1.03272 129.18 !!Species type (1 for dirunal, and 2 for semi-diurnal); constants (Reid 1990); the last 3 numbers are freq., nodal factor and arguments which should be same as those for the tidal b.c. (below)

S2 !! 2nd freq. name

2 0.113033 1.454441e-04 1.00000 0.00

N2

2 0.046398 1.378797e-04 1.03272 243.40

K2

2 0.030704 1.458423e-04 0.77955 310.55

K1

1 0.141565 7.292117e-05 0.90207 244.87

O1

1 0.100514 6.759775e-05 0.83992 247.06

P1

1 0.046834 7.251056e-05 1.00000 110.04

Q1

1 0.019256 6.495457e-05 0.83992 1.28

8 nbfr !!Number of constituents in tidal b.c.

M2 !!First freq. name

1.405189e-04 1.03272 129.18 !! freq., nodal factor and arguments; see [1]

S2

1.454441e-04 1.0 0.00

N2

1.378797e-04 1.03272 243.40

K2

1.458423e-04 0.77955 310.55

K1

7.292117e-05 0.90207 244.87

O1

6.759775e-05 0.83992 247.06

P1

7.251056e-05 1.00000 110.04

Q1

6.495457e-05 0.83992 1.28

2 nope

59 3 0 0 0 !Atlantic

M2 !First freq. (tidal b.c.)

0.808688 226.095786 !M2 amplitude and phase at 1st open boundary node

0.785793 225.374081

0.731786 224.540114

....

Q1 !last freq. for this boundary

0.017919 222.956272

0.017730 222.310333

....

0.012038 198.774149

0.011939 198.804927 ! Q1 amplitude and phase at last node

SCHISM utility site has some scripts to generate the amplitudes and phases for US coasts.