It is winter. With winter comes rain and with rain comes mud.  When the mud washes into the river, we get a muddy river which is a real problem for what gives it life – its mauri.  And then we have cars making mud by riverside parking!

Riverbanks are attractive.  The river calls to us and we love to sit to watch it or to wander along its banks marvelling at what its music and life does to our spirits.  Rivers that run through cities are significant to those who live near them, adding life and atmosphere that buildings cannot.

Rivers that run through cities create a planning issue: how close should the city creep towards the river’s edge?  In planned settlements, rivers are usually provided with a wide margin of recreational and ecological space on each side.  The green space created is usually a recreational area highly valued by the residents of the city.  In settlements, such as Christchurch however, early local government planning did not give much room for the rivers; they were viewed mainly as drains for the convenient removal of stormwater.  Subsequent infrastructure such as roads and sewerage were run along the riverbanks as convenient open routes thus increasing the city’s impact on the river.

And then along came cars with the need to park them along these roads and thus began the issue of cars, mud and riverbanks.

Road drainage by the river In a few areas, riverside roads have gutters that largely dissuade drivers from parking on the grass of the riverbank.  However, for the greater part of the river, there are no gutters or even bollards, to prevent the riverbank from being turned to mud by the frequent passage of car tyres in wet weather.

On some riverside roads, the camber of the road allows rain landing on the road to drain to the other side, be collected in gutters, fed into drains and piped to the river for dispersal. On many riverside roads, however, the camber naturally leads rainwater from the road to drain onto the riverbank directly where it can find its own path into the river.  Where such water percolates through sufficient plant matter, there is some small measure of protection for the river from the contaminants in the rainwater – sediment, copper and zinc from cars using the road.

Where the riverbank is too narrow and/or is already mud, however, there is no protection at all: the mud is quickly transported into the river.  The accumulation of this sediment intrusion along the river’s length combined with the far greater sediment flow from off the bush-denuded Port Hills means that during and after any reasonable rain event, the Ōpāwaho Heathcote River flows brown.  And that is a problem for the life of the river.

The latest Annual Surface Water Quality Report by the Christchurch City Council rates the water quality of the Ōpāwaho Heathcote River as “poor” with sediment a major factor in achieving that descriptor.

What can be done? Sediment enters the river from so many sources along its catchment.  The solution is always going to be incremental and long-term, but every step taken to reduce the sediment load will be a step towards the ultimate goal of improving the river’s health.

One step would be to reduce parking opportunities along the banks of the river by the judicial use of bollards, no parking restrictions, adequate provision of other parking spaces and the narrowing of riverside roads.  The recently published Lower Ōpāwaho Heathcote River Guidance Plan encourages these measures to go hand in hand with a widening of the riparian strip and increased native planting.  Both of these measures would help incrementally with water quality by increasing the filtering effect and by providing increased shade for the river.

By-Law prevents riverside parking  While judiciously placed bollards will be part of the answer, bollards the length of the river would be an unfortunate response.  It would be more effective, particularly more cost-effective, if drivers merely obeyed the City Council 2017 Traffic and Parking By-Law, clause 11.1 which states “A person must not stop, stand or park a motor vehicle, wholly or partially, on that part of any road which is laid out as a cultivated area, being a garden or a grass berm.”  It does not get much clearer than that!

Like similar by-laws, three things are required to make them effective in changing behaviour:

• education of residents about the issue
• placement of appropriate signage to remind busy people of the issue and by-law
• consistent, predictable enforcement of the by-law by the council

We encourage the City Council to activate its Traffic and Parking By-law to help reduce the sediment load in the river.