roadside ditch; gutter
Refers to a drainage channel along a road or path, typically covered or open, used to carry away rainwater.
大雨で側溝から水があふれた。
The roadside ditch overflowed due to heavy rain.
落ち葉が側溝に詰まっている。
Fallen leaves are clogging the gutter.
Compound of 側 (そく, 'side') and 溝 (こう, 'ditch'), literally 'side ditch'. The reading そっこう results from the assimilation of そくこう.