Talbot Herbarium. Wairau River - Large river rising in Spencer Mountains. It flows North between St. Arnaud and Raglan Ranges and then N.E. to the coast at Cloudy Bay: 105 miles in length. Wairau lower - 4 miles by road from Blenheim. Wairau upper - (see. Note: this field may have been truncated. Please check against voucher.