In former times, the Tai Po Kau Pier near Tai Po Kau Train Station was an important transport hub serving northeast New Territories.
As roads and public transport was improved in Tai Po and as the depopulation of remote villages. The station was abandoned when the railway was electrified in 1980s. With the completion of Ma Liu Shui Ferry Pier, the importance of the Tai Po Kau Pier declined quickly and used as Marine Police Pier.
Nowadays, the pier becomes a tide station of Hong Kong Observatory. If you notice Sai Kung North Rural is still a part of Tai Po District, which may closely related to the transport links in the past.
References:
蕭國健. 2007. 大埔風物志. 再版增訂. 香港:大埔區議會.(Sui Kwok Kin. 2007. The scenery of Tai Po. 2nd ed revised. Hong Kong:Tai Po District Council.)
Hong Kong Observatory. Location of tide gauges in Hong Kong.2013. [ONLINE] Available at: http://www.weather.gov.hk/tide/images/tide_map_e.gif. [Accessed 18 October 2013].