Question

how could you increase the frequency and decrease the wavelength of a wave in a marsh

Answer 1

Two useful relations you can use immediately are
- v = f λ (wave speed = frequency × wavelength),
- for shallow-water gravity waves v ≈ sqrt(g h) (g = gravity, h = water depth).

So to get higher f and shorter λ you can either drive the source faster (raise f) or reduce the wave speed v (so λ = v/f gets smaller for a given f) — doing both gives the largest effect.

Practical ways in a marsh:

1. Increase the driving frequency
- Make the disturbance oscillate faster: a faster paddle, a vibrating board, a boat prop pulsing more rapidly, or more frequent wind gusts. That directly raises f and (for fixed v) reduces λ.

2. Reduce the wave speed v
- Decrease water depth (drain or restrict flow locally); in shallow water v ≈ sqrt(g h), so shallower water gives a smaller v and thus a shorter λ.
- Increase bottom/vegetation drag: dense marsh grass, reeds, mud, or artificial roughness slows wave propagation and increases dissipation, which shortens effective wavelengths.
- Put barriers or closely spaced obstacles (stakes, sills) to break up long waves into shorter ones.

3. Use the capillary regime (for very short wavelengths)
- On very short scales (centimetres or less), surface tension matters and capillary waves dominate; a stiffer surface tension/shorter disturbances can produce shorter λ. This typically requires a small, high-frequency source.

Notes and cautions
- Slowing waves by increasing roughness or shallowing the water also increases damping — waves will lose energy faster and may become very small in amplitude.
- Very shallow or high-frequency waves can become nonlinear or break.
- Marshes are ecologically sensitive — physically altering depth or vegetation can harm habitat and may be illegal; avoid doing this in the field without permission.

If you want, tell me the scale of waves you’re interested in (centimetres vs. metres) and whether you can change the source frequency or the marsh depth/vegetation — I can give more specific suggestions.