Impacts on waterways
This resource supports our ‘Rivers and Us’, ‘Stream Sense’ and ‘Soils and Us’ teaching units. It includes a full colour PDF document containing pictures showing the impact of people’s activities on our waterways at three catchment levels. You can use the information provided on this page to discuss the issues affecting rivers, streams and the land that surrounds them with your students.
Use the PDF below to print out high quality, full colour graphics showing three waterway scenes: upper catchment, middle catchment and lower catchment. Each catchment level contains features which can be used to discuss the impacts of people’s activities on our waterways and the importance of protecting the natural character and biodiversity of our rivers, streams and surrounding land. The PDF features the three scenes as one picture, and each scene as a separate, larger picture.
The features in each picture and the issues associated with each catchment level are outlined in the three sections below. You can use this information as a starting point in discussing the pictures with your students.
Impacts on waterways showing a river at three catchment levels
(939 kb, 134 seconds to download, 56k modem)
This picture shows a typical upper catchment stream in a healthy condition. Many of the features (vegetation, rocks, the pool shape and slope) seen in this picture show how a wide variety of animal and plant life (biodiversity) are supported in this type of environment.
It’s also a good idea to think about what features resulting from human impacts on our waterways are not present in this picture (for example, vegetation removal, stock access and discharges).
The amount and location of vegetation (particularly trees) along waterway edges fulfils a number of functions (listed below) which help support other plant and animal life in waterways.
- Root structures provide bank stability (erosion control).
- This in turn improves water clarity due to stable soils not crumbling into the water. Clearer water enables aquatic prey and predators to see, navigate or hide.
- Shade from tree foliage lowers temperatures. High temperatures interfere with oxygen water uptake and the instream temperature range influences animal distribution. For example, if the temperature is too high (greater than 25 °C) then animals become stressed and die.
- Trees provide a habitat for animals living in and around the stream. What places can you see in the picture which would provide a home for these animals?
- Trees can be a food source for animals in and around the stream. For example, the branches lying in the stream.
- Different layers of vegetation at different levels combined with vegetation stability help prevent weeds, floral plant pests, leaves and debris clogging up the area and affecting native plant growth.
- Decaying matter provides another food source and contributes to the chemical balance of the soil.
- Tree canopies block rain, reducing run-off from surrounding land use.
- Bird life diversity is improved due to birds spreading seeds which increase new growth of native trees and shrubs.
Areas with a large number of trees also have a beneficial effect on the water cycle, including oxygen release (photosynthesis) and increasing the release/loss of water vapour to the atmosphere as moisture evaporates from tree foliage.
- Rocks of various sizes provide shade/shelter/protection for fauna.
- Erosion control is created by less mobile instream rocks and large rocks which provide bank stability. Rock composition also influences erosion rate and chemical balance of the water.
- The gaps between rocks provide habitat space and rock variety influences flow patterns in the water (slow, medium, fast), creating a choice of different habitats.
- Exposure to light and atmospheric moisture affects the amount of mosses/liverworts and algal cover present. These organisms are a food source for some of the animals living in and around the stream.
- Water flow is affected by the meandering nature of channel – how wide it is and its twists and turns. These channel characteristics offer many different niche options for aquatic life. For example, rapids (riffle), running water areas and calmer pool environments provide a number of different habit options for aquatic fauna.
- Typically streams have V-shaped channels (not visible in these pictures). This influences water speed and the level of stream bank erosion.
- The slope or gradient of the stream determines run off speed (visible as rapids or ‘riffles’) which enables oxygen uptake in the water.
- Natural high rainfall events. Water coming into and being retained in the upper catchment influences the time taken for peak water levels to be reached. These water levels also influence the rate at which water subsides further downstream. Poor use of the land (for example, widespread tree removal, inappropriate culvert installation) can lead to increased erosion and flood risks to land and property below.
- A large buffer zone between waterway and its surrounding land use provides a good natural filter of nutrients.
- Controlling or eradicating animal pests such as possums, ferrets and stoats helps to establish and maintain populations of mainly ground-dwelling native birds (for example, Kiwi). There is also less risk of diseases being passed on (for example, Bovine Tuberculosis).
- The steep gradient restricts people’s access to the upper reaches of the stream, lessening the chance of human activities impacting on the area.
This picture shows how biodiversity has been affected in some way by human activity which has changed the natural features of the stream (for example, farming). It is important to distinguish these effects from natural processes.
- Fewer trees around this stream means less shade and a rise in instream temperature. There is also more available light, increasing the growth of algae and other organisms that live attached to underwater surfaces.
- Fewer overhanging trees means less fallen debris for as a food source for animals in and around the stream. The soil’s chemical balance is affected and there are few shaded habitat areas.
- The water clarity is slightly less than that of the pristine stream. This is because there is a greater flow of water moving through the channel, stirring up mud and increasing the amount of suspended sediment in the water.
- The rolling hills in the background are an example of how geographical features can increase the chances of runoff with contaminants ultimately ending up in the stream.
- The exotic (non-native) forest in the background demonstrates land uses which aren't ‘environmentally’ suited to dairy herd or dry stock grazing and represent a quick 'remedy' to land stabilisation (particularly near headwaters).
- A buffer zone showing riparian planting between land use and the water demonstrates the value of blocking nutrients from runoff (particularly Phosphorus which is bound up in sediment). The plants along the banks of the stream take up the nutrients instead outside the instream environment.
- The banks are still stable as the hardy Carex-like grasses are able to withstand high water levels yet still bind the soil together.
- Rocks in this section of the stream are smaller in size in comparison with the pristine catchment, due to natural abrasion. However channel alteration can influence flows which in turn affects the natural erosion rate.
- Most rocks are of similar sizes, limiting the variety of instream habitats.
- The habitat is less stable because smaller rocks are more mobile.
- There is greater water flow in the stream at this catchment level due to other streams flowing into it (tributary contribution). This leads to higher erosive energy along the streambanks, threatening stability.
- Some twists in the stream’s path (‘meanders’) are still apparent, providing variable habitat to animals in fast, slow, deep and shallow flow areas. Discuss how animals also adapt to these conditions, for example, mayflies and stoneflies that thrive in fast flows have flattened bodies.
- Nutrient and sediment runoff into the stream is increased by the number of contributing tributaries within the catchment, particularly by those not protected from runoff themselves.
- Note that dairy stock are fenced off from the stream, preventing effluent getting directly into the waterway.
- Waterways which are surrounded by land easily accessed by people can suffer from the effects of related activities. For example, nearby houses, roading, quarrying, water extractions (irrigation), water discharges (treated effluent systems) and the possible introduction of plant and animal pests such as mosquito fish and rats.
This last picture shows features common to rivers (not streams) nearing the coast.
- This river contains a large volume of water from all contributing tributaries. High flows can have flooding risks for urban areas nearby. Flooding issues to consider include stopbanks and flood gates.
- The lower land gradient results in water lying around for significant amounts of time. Consider how flooding issues relate to land use considerations.
- This river’s water is murkier than that of the other two catchments. This is caused by the change in substrate (mainly sand/silt substrate) which is highly mobile.
- There are less trees and shrubs on the banks, increasing water temperature and instream productivity.
- Inherited problems (from upstream tributaries), for example, sediment load from upstream erosion and high number of discharges to water.
- This picture also highlights the importance of wetland type flora to birds and native fish species.
- Stock exclusion is also depicted and the flatter nature of the land contour has implications for runoff.
- Water velocity and possible tidal (saline) effects may affect river fauna and flora.
- Discuss flood prevention measures (flood gates, spill-ways and stop banks) (not visible in this picture).
- Discuss how native fish migration can be assisted. For example, clear passage throughout the waterway allows fish to get through to the upper catchment while perched culverts hinder them.
- The tidally influenced riverbank habitat is vital in sustaining the life cycle of native fish. For example, adult Inanga, Kokopu and Koaro lay their eggs along these banks. These eggs hatch into juveniles (generically called ‘whitebait’ during this phase) which grow into adults as they migrate from the sea to the upper tributaries.
- Increased recreational use can affect a river, stirring up sediment and disturbing animals and plants in and around the river area.
- Flow characteristics are very similar – mainly ‘run’ type flow.
Disclaimer: This resource is out of date. The curriculum links are not current. However we believe the content and activities are still of value to teachers.