Written consent under a municipal by-law must be obtained from a person delegated to exercise powers under that specific by-law, having regard to the considerations addressed in that by-law. Historic planning approvals granted under different legislative regimes before the by-law came into effect cannot constitute the requisite consent under the by-law. Environmental protection by-laws that prohibit future conduct affecting stormwater systems without consent operate prospectively, not retrospectively, requiring new consent for activities undertaken after the by-law's commencement even where earlier approvals existed. In interpreting environmental directives, technical terms with distinct scientific meanings such as 'wetland' and 'floodplain' must be given their ordinary meanings and not treated as synonymous, particularly where the directive itself clearly distinguishes between them in language, context, and remedial measures required. A floodplain extends to the specified flood level (here 1:100 years) while a wetland is a distinct ecosystem that may be smaller than the floodplain.