Environmental Impacts of Sand Mining from the beach at Whiritoa, Coromandel Peninsula

Whiritoa Beach is a small pocket beach on the eastern coast of the Coromandel Peninsula. In 1977, beach sand was being mined from the southern lagoon at approximately 4000 m3 per year. Recent subdivisional development of the dunes at Whiritoa Beach increased the public use of the beach, resulting in a multiple use management problem concerning the influence that continued sand mining was having on the beach’s stability. Whiritoa sands are well sorted medium sands which are dominantly comprised of quartz, feldspar and volcanic glass. This study undertook weekly profile transect measurements for 12 months, and showed that the volume of beach sand was 162,000m3 on 7/2/74. At maximum recession the beach volume was reduced to only 50,000m3. This study concluded that as Whiritoa is believed to be a “closed” system, continued mining could remove the beach volume in only 13 years. This study therefore recommended that the sand mining operation at Whiritoa Beach should cease. Purpose: The study aimed to evaluate the stability of Whiritoa Beach and determine beach and/or dune recession that may be occurring as a result of sand mining. Identify sediment characteristics in various beach environments and use mineralogical analysis of beach sediments to test the hypothesis that Whiritoa Beach is a closed system isolated from coastal littoral drift. Determine the significance of cliff recession as a source of sediment for renourishment of the beach system. Investigate seasonal variations in sediment and weekly variation in the volume of sediment above low water mark. Investigate non seasonal patterns of change in beach volume and estimate the sediment reservoir in the beach system.

Textural sediment analysis of “summer” and “winter” beach conditions, and textural trends within and between beach geomorphic units. Mineralogical analysis determined percentage range of hypersthenes, hornblende, magnetite, cummingtonite and augite found in the Rotoehu Ash, the Beeson’s Island Volcanics, the Minden Thyolites and the Whiritoa Beach samples. This was undertaken to determine beach sediment sources. Also determined content of quartz, feldspar, volcanic glass. Also assessed mineralogical content of adjacent beaches (Whangamata and Mataora). Also determined calcium carbonate content by digesting in dilute hydrocholoric acid. Chapter 5 - an assessment of wave climate at Whiritoa Beach Chapter 6 – the influence of waves and winds on Whiritoa Beach. Chapter 7 – Sediment budget in response to changes in wave characteristics. Five beach profile sites established and monitored along Whiritoa Beach. Calculated volumetric change. Chapter 8 – assessment of sand reservoir preservation potential under pressure of continued sand mining.

Whiritoa Beach, eastern Coromandel Peninsula. Some investigations on neighbouring beaches (Whangamata and Mataora).