Motu Catchment

• Geology and geography of the catchment
• Land use in the catchment
• Flood risk management in the catchment
• Significant floods in the catchment

Geology and geography of the catchment 

There are three main geological groups that make up the western half of the Motu catchments, these include Holocene Deposits, Quaternary Deposits and the Urewera Group. Holocene Deposits are mainly found in the lowlying coastal flats and along river flood plains. The Quaternary Deposits here are found mainly in the coastal foot hills. The Urewera Group is by far the largest geological group found in the whole of the catchment and makes up the steeper hill country.
The eastern side of the catchment is a little more varied, like the western side it has three main geological groups, the Urewera Group, the Karekare Formation and the Waitahaia formation as well as a smattering of other geological groups.

* The set of information was incomplete for this area, some areas may vary from that noted above.

Within this major catchment there are three small coastal catchments, Omarumutu, Pehitaihi and Whituare, these catchments are made up of many short, small streams that feed directly into the ocean. There are also a number of more significant catchments including the Tirohanga Stream catchment, the Waiaua River catchment, Torere River catchment and the Hawai River catchment. By far the largest and most significant catchment within this major catchment is the Motu River Catchment itself.

Coastal catchments

Coastal catchments within the Motu major catchment are made up of many small streams and overland flow paths that drain directly into the ocean, most are short and have few or no sub-catchments (smaller branch streams).
The coastal catchments in the motu area contain most of the lowlying coastal land within the Motu major catchment apart from the lowlying land around each of the river mouths.

Minor catchments

Tirohanga Stream
This catchment is extends some 10km inland from the coast, the further most extent of the catchment reaches a maximum elevation of around 330m. The eastern and southern parts of the catchment are steep hill country covered with bush, the majority of the catchment is flat to rolling hills with significant floodplains surrounding the Tirohanga stream. These areas of productive land are used for farming and horticulture. There has been some flooding in the catchment with lower lying farms being partly inundated.

Waiaua River
The Waiaua catchment is 14km long, the river flows out of mountainous land covered in forrest, where it grows as streams join it adding to the flow, 6km inland from the coast the river reaches an area of floodplain now farmed, the flood plain ends as the river squeezes between two hills before opening out again. From here the flood plain gradually widens untill it reaches the coast. The foot hills that surround the flood plain are also user for farmland in places. 

Torere River
This catchment is 13km long and two thirds (8km) as wide, around 100m above the Torere river mouth the Waiti stream joins the river, further upstream the Torere river has a number of streams that flow into it, these stream branch out to the right and the left contributing water to the river and creating a relatively short wide catchment. The inland three quarters of the catchment are steep to mountainous hills, with a maximum elevation reaching 630m above sea level. These hills are covered with native and some exotic forestry, with evidence to indicate some slips. The lower reaches of the river flow through steep to rolling hillcountry before reaching the floodplain, flowing through the farm land and entering the sea next to the small Torere community.

Hawai River
This catchment is prodominantly steep to mountainous hill county, reaching a maximum altitude of 969m above sea level. Tributaries flow though the numerous valleys, all eventually join up with the main Hawai river which meanders through the catchment before flowing out to sea at Hawai. There is a small area of floodplain near the coast (around 150 acres), this very quickly becomes steep hill country. Most of the catchment in native forest, with some exotic forestry in the hills near the coast, and a number of pastural paddocks in the floodplain.

Motu River

The Motu River catchment is an area of mostly mountainous land on the north-western slopes of the Raukumara ranges. Near the eastern catchment boundary a maximum altitude of 1475m is reached (Puketauhinu), the catchment has many steep peeks and ridges over 100m above sea level.
The river itself is 147km long with the upper 50km meandering across a pastoral floodplain, where the village of Motu is found. From the Motu falls to around 10km from the mouth the river falls 300m in elevation over 50km making it popular for rafters and canoeists.  The lower reaches of the river are bordered by gravel beaches, with the last 5km of river taking on a braided river pattern.

Land use in the catchment

The catchment is almost all forested, most of this being native, although patches of exotic forest are also present. The coastal lowlands, river floodplains and the surrounding foothills are farmed, with some land also used for horticulture and several small communities. The main commumities include Tirohanga, Opape, Torere, Maraenui and Motu Village, the first four of these are coastal communities with the Motu Village being 33km inland on an area of floodplain in the upper reaches of the Motu river. 

Flood risk management in the catchment

There are no Bay of Plenty Regional Council maintained river schemes, drainage schemes or assets in this area.

Significant floods in the catchment

 Flooding through this area is not uncommon, the Motu area can recieve very high intensity rainfall in the ranges bringing floodwaters through the catchment. Lowlying farmland can become inundated from time to time. As there are few residential dwellings in the area the consequences of flooding in this area is mainly restricted to damage to farms and crops, although rising floodwaters in the catchment can be a hazard for people in the bush hunting or for recreational purposes.