Gold dredging began in the late 1800s as a way to extract gold from rivers and streams. The California Gold Rush of 1849, which brought a large number of people to California in search of gold, led to the development of new and more efficient ways to extract gold from the earth. One of these methods was dredging.
The first dredges were powered by steam, and were developed in the 1850s. These early dredges were relatively small, and were typically used to dredge small areas of a river or stream. They were not very efficient at extracting gold, and could only process a small amount of sediment at a time.
In the 1870s, new dredging technology was developed that made it possible to extract gold from larger areas of a river or stream. These new dredges were powered by gasoline or electricity, and were much larger and more powerful than the earlier steam-powered dredges. They were also more efficient at extracting gold, and could process a much larger amount of sediment at a time.
The first dredge with a floating dredging platform was built in California in 1884. The dredge was equipped with a long boom, which was used to scoop up sediment from the riverbed, and a series of sluice boxes, which were used to separate the gold from the sediment. The dredge was able to extract gold from much deeper in the river than previous dredges, and it was also able to process a much larger amount of sediment.
The first successful gold dredge in New Zealand was built in 1894 in the Grey River, West Coast. It was the first of many dredges that would be used to extract gold from New Zealand's rivers and streams.
Dredging technology continued to improve throughout the 20th century, with larger and more powerful dredges being developed. Today, dredging is still used to extract gold and other minerals from rivers and streams, but it is also used in other industries, such as construction and sand mining.
It's worth mentioning that gold dredging can have negative effects on the environment, by causing sedimentation, altering water chemistry, impacting aquatic habitats and fish populations, and releasing mercury used in the extraction process.