1N-PLURAL 河段;流域;(上、中或下)游 The upper, middle, or lower reaches of a river are parts of a river. The upper reaches are nearer to the river's source and the lower reaches are nearer to the sea into which it flows. 河段;流域;(上、中或下)游
This year water levels in the middle and lower reaches of the Yangtze are unusually high. [+ of]
长江今年中下游的水位都过高。
2N-PLURAL (外)围;(远)处 You can refer to the distant or outer parts of a place or area as the far, farthest, or outer reaches. (外)围;(远)处 [formal]
...the outer reaches of the solar system. [+ of]
太阳系的外围
...the farthest reaches of Cambodia.
柬埔寨的最边远地区
3N-PLURAL (组织或机构中的)层级 You can refer to the higher or lower levels of an organization as its upper or lower reaches. (组织或机构中的)层级 [formal]
...the upper reaches of the legal profession. [+ of]