Tidal Flat
Tideland
noun
A dry lagoon is a tidal flat.
ひがた
The reading for 干 is an exceptional one. Just think to why the lagoon is dry. It's because of the heat (ひ) of the sun. Watch out for the rendaku.
交際一ヶ月記念の日に、干潟に潮干狩りに行ってきたの。
We went to a tidal flat to go clamming for the one month anniversary of our friendship.