tunnels
preferred label: تونل @fa
type: Concept
related: gravel tunnel drains

drainage
preferred label: زهکشی @fa
type: Concept
narrower: gravel tunnel drains
related: gravel tunnel drains

gravel
preferred label: شن @fa
type: Concept
related: gravel tunnel drains

gravel tunnel drains
related: tunnels
related: gravel
related: drainage
broader: drainage
preferred label: زهکش‌های تونل شنی @fa
type: Concept