Taking Measurements

Where to take measurements

Measuring physical conditions

Measuring biological conditions



Where to take measurements

River investigators need to take care as conditions can be unsafe near or in rivers. Select your sampling stations in localities that are easy to get to and that represent a range of habitats and conditions. The stations are established by the preliminary survey and the monitoring plan.

Each measurement must be taken from a standard site, and using standardised equipment to be comparable with earlier and later records.

The measuring stations need to be recorded as word descriptions and as drawn site plans so that the long term monitoring programmes, that necessarily employ different samplers, will have useful comparable data.

Example : "Flow rate measured from Green Park footbridge to Main Highway road bridge with flow indicator floats dropped from the centre of the footbridge (beside the 9th handrail support from the northern side)"

Measurements of Physical Conditions

There are a great variety of data that could be collected from any waterway. These are ones that are meaningful yet easy to collect. In addition to these, chemical tests of phosphates and nitrates are important, but require handling chemicals and/or purchase of expensive equipment. The instructions for taking phosphate and nitrate measurements accompany the particular kit used. The tests are arranged in order of ease of conduct and the long-term value of taking them.


Of all the potential measurements, photographs of the sampling sites have the greatest long-term value and cover the widest range of information with the least amount of effort. It is vital, however, that the photographs be made so they can be shot again in exactly the same way from the exact same position in the future. This means recording the location, angle, time, date, and specific landmarks so anyone can return to the site in later years and snap a comparable shot.

Each particular site will need at least three views (video can also be used, but be sure to make a duplicate tape and store it in a dry moisture-proof container in a cool location). Take an establishing shot that shows the whole area, including landmarks that are likely to be visible in later years. Have a member(s) of the team stand at the site where the next image(s) will be taken. Then take a medium range shot of the place where the samples will be taken, again showing team members actually taking measurements, and indicating where the close shots will be taken. Finally, take a close shot(s) of habitats of special interest.

Each photograph should be identified with the river name, station number, date, photographer, and any relevant comments. They should then be mounted in the log book and the information giving detailed descriptions and drawings of how and where they were taken written next to them. If video is used, the person taking the video or an assistant should verbally record information on location and other descriptive information while the images are being taken.

Some groups may be able to scan or video-capture the images and put on computer for a database.

The photographs are especially important because some aspect of the river might change that was not measured or even thought of during the survey. They also can capture changes that are extremely difficult to measure or describe in words.

Water colour

Against a paint colour card, or a series of plain colour transparencies, record the colour of the stream by card name and number. This can be an important and easily obtained indicator of river health and is suitable even for primary school children.


Though people do not have such sensitive powers of smell as some other mammals, like dogs, we are still good at distinguishing and recognising different smells. The smell of a water sample can often serve as a useful record of its cleanliness or pollutants. Have several members of the group smell the water and secretly write down a description of the smell before disclosing what each smell sampler's comments. The human nose can easily distinguish smells which are oily, peaty, mouldy, or smell of rotten eggs (marsh gas / hydrogen sulphide) cow shed waste, sewerage, rotting animal flesh or rotting plant matter.

Smell descriptions can be a useful clue of stream water quality.


Use either a glass thermometer or electronic probe.

The bulb of a glass thermometer (ideally in a damage protection sleeve) must be in the water while the thermometer is being read. In small streams this can be done from the bank or by standing in the stream at a set distance from the bank. In rivers it is necessary to take a sample of water using a weighted bucket on a rope and measure the water temperature of the water in the bucket

An electronic temperature probe can be suspended in the water if the lead is long enough, and provides instant readings.

Acidity / Alkalinity (pH)

On a 14 point pH scale, water that is neither acid nor alkaline but is neutral, measures exactly 7. Measurements lower than 7 are acid (vinegar has a pH of 3) and higher measurements are alkaline (such as bleach which has a pH of 13).

Unpolluted stream water may naturally be slightly acid (measuring between pH 7 and 6) if it has drained from peaty ground or slightly alkaline (measuring between pH 7 and 8) if it has run off limestone country. Higher or lower values are generally caused by pollutants in the water.

Many freshwater creatures are very sensitive to pH levels.

Acidity / alkalinity is measured with either a pH meter or pH indicator paper which changes colour according to the acidity / alkalinity. The electronic meters are much more sensitive than the paper and are easier to read. The paper, however, is inexpensive and may be used for preliminary measurements.

Turbidity / Clarity

This measure gives an indication of the amount of suspended solids, natural or artificial dye substances and / or the density of suspended plant plankton in the water.

Turbidity is measured by lowering a weighted marker disc on a graduated line into the water. The depth at which the disc becomes invisible is recorded.

A standard disc, known as a "secchi disc", used for these measurements is a metal plate with alternating quadrants painted black and white.

Secchi disc measurements give easily comparable measurements of water turbidity for lakes and the sea where the water is deep but in stream the water is frequently not deep enough. Where this is the case horizontal secchi disc measurements can be taken. Fix the disc to a pole and view it horizontally underwater through a simple, single mirror periscope. Move the disc away from the observer until it can no longer be seen and record the exact distance.

Water Height

In summer when evaporation from the land exceeds rainfall there is little run-off and river levels are low.

In winter when rainfall is high and the ground is saturated run-off is rapid and river levels rise quickly after heavy rain.

Well managed water catchments which retain good amounts of forest cover on the land have less extreme variation between summer lows and winter highs and are less subject to sudden large rises in water level because the bush acts like a sponge to delay run-off. Water catchments which have land stripped bare of forest for agriculture, horticulture or industrial and residential development cannot delay run-off and experience flooding in winter and dry streams in summer.

Water level is a good measure of catchment stability. It can be measured against a water level staff fixed to a bridge support in a position where it is always easily read.

Make it from tanalised 100 mm wide board painted white with black graduations.

Flow rate

Flow rates vary enormously along a river depending on volume of water running down and the depth and width of the channel at any particular point.

Flow rate is also variable across a river. On a straight stretch it is greatest in the deepest part, usually in the middle and least near the banks on each side. On a bend it is slowest on the inside of a bend and fastest on the outside. This often leads to the outer bend being cut away and to sediment collecting on the inner side of the bend.

Electronic flow meters can be used to measure flow rate but are expensive, need to be mounted or held on a boom in a standard manner to give consistent and useful measurements.

Surface flow measurements can be made by dropping floats into the river and timing how long it takes for them to travel over a standard measured distance. This may be from one bridge to the next or it may involve teamwork with one person dropping the float from a bridge and another, down stream recording when it passed between "Ideally these posts should be natural (eg. two trees) or artificial but permanent (eg. two fence posts) but it may be necessary to used two marker poles fixed in each bank specifically for the purpose. Such poles are more likely to be vandalised, damaged by cattle or washed away during floods and are therefore less satisfactory.

The floats must be clearly visible. Ideally they should be recoverable especially if not made from natural materials.

Oranges, lemons or grapefruit make very good flow recorder floats. They are very easily seen and will eventually decay harmlessly if lost downstream. They also have the advantage of being only slightly less dense than water so they float up to the water surface and not on top of it. Floats that are very buoyant (like empty plastic bottles) can be subject to windage (= being blown along, backwards or across the river by wind) which reduces the accuracy of the measurements.

If plastic bottles are used as flow indicators they should be partly filled with water so that they float in the water like an orange or a cormorant rather than on it like a boat or a duck.

Tethered floats. A practical method of using plastic bottle flow measuring floats is to tie them to fine fishing line that is loosely coiled at the drop station on the bridge or bank. When a tethered float has travelled a measured distance it can be hauled back for repeat runs by different members of the group giving opportunity for all to drop, watch the finish, time the run and record the results. Having the float on a line also allows it to be dropped precisely at the same spot on each trial by lowering it close to the water and releasing on the timers call. A flag marshal down stream signals the completion of each run for the timer and float retriever.

Light levels

The amount of light passing down into a stream greatly affects the wildlife found there. Animal life flourishes where the water is overhung by leafy trees and becomes scarce where riverside vegetation has been removed and the banks "cleaned up".

This partly because in small streams or in slow moving shallow water at the edges of large rivers, the water can become much hotter on sunny days. Warm water can hold much less dissolved oxygen than cold water. The amount of oxygen that can be dissolved in water is halved when the water is warmed by 10 C.

Some cold blooded animals become more active as temperature rises and therefore need more oxygen. In slow moving water oxygen replacement through the surface may be insufficient on warm days and the aquatic wild life may suffocate.

High light levels also make small invertebrate animals much more visible for predators like wading birds and certain fish.

Baseline light levels should be measured right across a river from bank to bank and plotted against distance from the banks. A simple photographic light meter can be used, held just above water level as it is carried across the stream. For fast flowing streams the measurer should, for safety, be loose shackled to a rope stretched tightly across the river. The rope should be boldly marked off at one metre intervals with permanent pen or paint marks and light readings called out to a recorder on the bank.

If bank vegetation changes from one year to another - due to bank bush being removed or to a bare bank being planted with trees - changes should be expected to the river's wildlife.

Measuring Biological Conditions

Biological Indicators

Freshwater plants and animals are an excellent indication of the health of a waterway. They are a more reliable index of water health than physical parameters because while physical parameters can change rapidly the animal population must remain there for some time, thus indicating the long term physical conditions.

Stream and River Plant Life

Macrophytes - Large plants

To appreciate the diversity and learn some of the names of pond and river plants, it is useful to make a class collection. This can be stored and presented as a herbarium collection or ideally for younger scientists as a large wall poster in which the specimens are arranged in appropriate sites, depths and relationships on a sectional background drawing of a stream or pond.

Water plants make excellent biological indicators. The New Zealand Ministry for the Environment has published water quality quidelines with colour photographs of algal conditions that indicate various stages of waterway pollution. Copies of these quidelines are available from the ministry at a small cost.

Mounting water plants for reference and display. As most water plants are soft and flexible they are easy to layout, dry and display.

Microscopic plants.

Rivers, streams, and lakes are filled with microscopic plants. When rivers receive too many nutrients, these tiny plants bloom in tremendous numbers and colour the water a vivid green or brown with their small bodies. Using them as an index of water quality is difficult without a quality microscope and some specialised equipment. There are two ways to collect and measure microscopic water plants.

Diatometers are simply microscope slides placed in the water for a day or two and then removed and examined under a microscope to see what has settled on them. A diatometer is easy to build.

Cut a short piece of plastic pipe (18 to 25-mm in diameter, about 300-mm long) about half-way through in a series of six horizontal notches. This is quite easy to do with a small saw. Bend the pipe back, away from the cuts, to open the slots and put the microscope slides into the notches. (The slides should be numbered with a felt tipped pen so you can identify them later). When the pipe is released, the plastic grips the slides, providing a horizontal rack. Carry the pipe and numbered slides to the waterway to be investigated and assemble the diatometer just before placing it in the water. Push one end of the pipe into the sediment of the stream so the rack of slides is below the water but above the sediment. Record the exact time and location of placement, along with the numbers on the microscope slides. You might want to have three or four diatometers to place in different habitats of the waterway. After two to three days, the slides will have a thin settlement of plankton that can be looked at under a microscope.

Diatometers are highly quantitative and it is easy to repeat the measurements to compare conditions at different times of the year or under different circumstances. You can do two different measurements from this collection. Identification of the diatoms or other algae is one measurement. This requires having an identification manual.

Secondly, and perhaps easier, is to count the number of cells within a specified area. Ideally, you might be able to get a measuring grid reticule from a hospital of the type used to count blood cells under a microscope (this might be difficult as these days blood counts are usually done electronically). Otherwise you could simple pick a suitable magnification and count the cells within one field of view, then shift the position of the slide and count again. Count at least 10 views on each slide and average the results to obtain an average number of cells per view. Be sure to record the exact magnification of the objective and eyepiece used. If possible, directly measure the size of the field of view using a standard grid and record the data as number of cells per square millimeter.

Stream and River Animal Life

Freshwater animals are numerous but secretive. Most are difficult to see in their natural environment and many are equally difficult to catch. Some can be found clinging to boulders - usually the undersides and some are fairly easy to trap in nets if they can be disturbed. Many stretches of swiftly flowing streams have rather small amounts of wildlife that is easily trapped. Some animals (birds and fish) are only seen but not caught but still need to be recorded.

Wildlife go to rivers and creeks to drink. There are many other animals that make their homes on river banks or in rivers. You will never see the larger creatures unless you make a special effort. From the resident's point of view, human beings are the most dangerous, wanton killers imaginable. Almost every wild creature on the planet - even tiny birds - flee at the first sight or sound of human beings. But they can get to know individual people and eventually learn to trust them.

Just as a pet dog or cat will let you approach, wild birds and other creatures will gain confidence and trust around individual people who don't make loud noises or act aggressively. Sometimes, if one or two people sit quietly - without talking - and observe, the creatures will begin to go back to their own affairs.

People who do wildlife photography, especially of birds, often build a "blind" where they can sit out of sight of the wildlife. Sometimes they will have a friend or two enter the blind with them. The friend(s) then leave the photographer alone in the blind, so the birds - which are watching very closely - will think the people have left. They are not good at counting.

Bacterial counts, especially of fecal Coliform, are an important measurement of the health of a waterway. Sampling for fecal Coliform bacteria requires special equipment and sampling techniques. Details of taking these measurements are available from the manufacturer of kits for measuring and culturing bacteria. There is a new system for measuring sewage pollution using an enzyme reaction test that makes the process much simpler.


In shallow slow flowing creeks where it is safe to stand in gumboots in calf deep water, animals can usually be disturbed from the bottom by gently shuffling about in the gravel and mud.

Hold a trap net about half a metre to a metre down stream from where the bottom is being disturbed to trap small creatures carried away by the current.

The net of tough nylon should have a fine 2 mm mesh size and be fixed to a sturdy frame of aluminium strip. This can be bent easily to shape and if required can be reshaped in the field so the opening is flat at the bottom or rounded to suit the shape of the bottom.

Items trapped and washed down into the end of the net are released by turning the end inside out in a white plastic tray containing a little water. Shake the net gently in the water to release the animals.

(An ice cream carton can be used for a tray but a larger, shallower tray is better).

Hand gathering

Using fingers or tweezers small animals can be picked off stones and submerged or bankside logs or along clean firm stony stream beds. These are such creatures as small snails (especially Potamopyrgus antipodarum ) the fresh water limpet Latia neritoides and caddis fly larvae in their various cases.


A variety of traps can be used to catch elusive river critters. A small collection of river rocks, placed in a chicken-wire basket will become a home for lots of small insects and worms if left in the water for a few weeks. Tie the basket to a length of fishing line so you can retrieve it. The most difficult part of this method is to be sure where you left it so you can find it again. The second most difficult part is hiding it well enough that someone else will not come along and disturb it out of curiosity.

Koura, or freshwater crayfish, are easy to trap and can be a useful biological indicator.

Sorting and identification

From a standard identification sheet or book sort and count the different animals collected. It is important that all members of the class or group are given plenty of opportunity to inspect the animals caught and to relate them to drawings on ID sheets. They are then more likely to be familiar with what was in the stream when the exercise is discussed later.

Establishing a reliable database is dependent on accurate identification. A method may be needed to verify that participants are correctly identifying and counting their catches. Small insect larvae are frequently difficult for experienced students to separate and identify. It may be necessary to limit the observed creatures to general categories in the first stages of the investigation.

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