Major catchments
What
is a catchment?
A catchment is an area of land, bounded by natural features such
as mountains and hills. A catchment boundary is defined by the
direction in which water would flow at any given point and which
river, lake, wetland or stream it would end up in.
Water that falls into the catchment will make its way as surface
water or subsurface water and eventually flow into the streams,
rivers, lakes and wetlands within the catchment. Water flows
downhill taking the shortest and easiest route possible, collecting
in the lowest lying land in any landscape; this is where you will
typically find streams, wetlands, lakes, and rivers.
Click for more detailed information, also a good classroom resource.
Why catchments matter
What happens within a catchment affects the life and health of
that catchment. If a drop of water falls onto the land high up in a
catchment it will be transported down the catchment through the
soils and water bodies within that catchment, meeting up with other
drops of water as it travels to the mouth of the catchment, this is
often where a river meets the ocean or where a stream flows into a
river.
The amount of rain to fall in one catchment will not affect the
neighboring catchment, even at the edges of the catchments. What
happens within a catchment usually stays within that catchment. For
this reason we need to be aware of the catchments around us and
what is happening within them.
Different catchments behave differently due to their size, shape, topography (how mountainous it is), soil types and land cover. All these factors contribute to how a flood will flow, grow, behave and affect people living within the catchment.
- Small catchments with few sub-catchments will have a shorter response time to heavy rain, the time it takes the water to flow into the streams and rivers is relatively short, and the waterways within the catchment will rise, peak, and fall again once the rain stops, in a relatively short space of time.
- Larger catchments take a longer time to return to normal after a heavy rainfall event. Larger catchments mean longer travel times for water to get from the farthest extents to the mouth. For example on average it takes the peak of a flood 6hrs to travel from Waimana gorge recorder situated on the bank of the Waimana River in the gorge to the Valley Rd flow recorder situated about 13.2km upstream from the mouth of the Whakatane River, a distance of around 18.5km.
The nine Bay of Plenty major catchments
See links below for more information on the major catchments within the Bay of Plenty Region.
