Stream Flow Monitoring
Stream discharge can be monitored using a variety of techniques. The most common method is the use of a stage recorder, which measures the height of water above a stream bed. Discharge is then derived from the streams associated rating curve. This curve is the manually established relationship between the elevation of the river and its discharge. Discharge must be directly measured to establish this curve. Discharge is typically measured manually with the use of a flow meter, wading rod, and tape measure although the conductivity meter has recently become an option.
Flow Meter
The flow meter is the standard instrument by which stream velocity is measured and discharge is determined. It consists of an adjustable wading rod, calibrated steel shaft, a flow meter (a series of cone-shaped cups attached to a rotating collar), and an electronic beeper or counter. The flow meter is attached to the wading rod and the beeper to the flow meter. Either one or five revolutions of the flow meter result in a beep or iteration of the counter. Every flow meter is calibrated so that the number of revolutions per minute can be converted to stream velocity using a chart or regression equation.
Determining Discharge
A stable stream cross section is divided into a number (8-10) of smaller units of equal width and uniform bed conditions. Velocity is measured at 60% (from the surface) of the depth of each unit and then multiplied by the unit area to give the unit discharge. Total discharge is the sum of the discharges of the smaller units. This procedure allows for discharge measurements of channels with irregular profiles.
The wading rod is graduated in 2, 10 and 50 cm increments marked with single, double and triple bars, respectively. The square sliding rod has 4 cm increments, however, they are labeled in decameters. Since 4/10 is the standard depth of the flow meter above the stream bed, sliding the square rod until the current stage is opposite the mark on the upper end of the wading rod puts the flow meter at the standard elevation. The marks on the upper end of the wading rod represent cm intervals, such that the elevation of the flow meter can be set to the nearest cm.
e.g. If the depth of the stream is 50 cm, then the 5 dm mark on the sliding rod should be opposite the 0 cm mark on the wading rod. The flow meter will now be at 20 cm on the wading rod (4/10 of the distance from the stream bed to the water surface).
e.g. If the water depth is 88 cm, then move the sliding rod until 8 dm is opposite the 8 cm mark on the top of the wading rod. The height of the flow meter will be 35.2 cm (4/10 of the stream depth).
Sampling of Stream Sediments
The sediment load of streams consists of dissolved and suspended sediments and the bedload. The bedload remains in contact with the bed of the stream, usually moves only during high stage (floods) and consists of the larger clasts (pebbles, cobbles, gravels and boulders). Therefore bedload sampling does not require sampling of the water, but rather the direct measurement of the bed materials.
Because the other mineral sediment is either suspended or dissolved in the stream, the water itself must be sampled to determine the suspended and dissolved sediment loads. The quantity of dissolved mineral material is the water hardness or Total Dissolved Solids and can be determined from any sample of flowing water. Whereas these materials are in solution in the stream, the concentration of sand, silt and clay are suspended in the turbulent flow varies thought the cross-section of the stream. It increases with depth with most of the suspended sediment being transported near the stream bed. Therefore, for the purpose of suspended sediment sampling, water is collected either from specific depth or more often vertically through the cross section using a depth integrating suspended sediment sampler.
The depth integrating sampler consists of streamlined housing for a one-litre bottle connected to a wading rod (a graduated metal pole). The open mouth of the bottle is held tightly again a rubber gasket. The water enter through a small hole in the housing. The hole is threaded to accommodate plastic nossles of various diameter, so that at which the bottle fills can be controlled. That is, a wide nossle is used in slowly moving water and a small diameter nossle is used in swift water. The objective is the fill the bottle with one-litre of stream water obtained from the entire depth, by slowly lowering the bottle, with the nossle facing upstream, from the surface to bed and back up to surface over a period of 60 seconds. Some practice is required to achieve a rate of water sampling that ensure that sediment has been collected from the entire depth. That is, the bottle should be full only just before it has been lifted from the stream.
Try to avoid disturbing the stream bed with sampler or your feet, as this will generate suspended sediments. Two one litre bottles of water constitutes one sample for a given time and cross section. Observations include the depth of water, time of sampling, duration of sample, sample number. These data a placed on the bottle and on cardboard insert (pog) that fits in the mouth under the lid. In the laboratory the sediment if filtered from the water and weighed and expressed as a load (mass) and sediment concentration (mass/volume of water). Particle size analysis (% of sediment in various size classes) it the two bottles contain more than a few grams of sediment.
The Direct Measurement of Water Hardness (Total and Calcium)
The disodium salt of ethylenediaminetetra-acetic acid, or 'EDTA', forms stable complexes with calcium and magnesium ions. This reaction is used as the basis of simple volumetric procedures for determining water hardness. Calcium and magnesium ions are titrated with EDTA, using indicators which themselves form coloured metallic complexes. This method, which is simple and easy to apply, can be employed on all water samples and is especially useful in its application to waters of low hardness. In recent years it has largely replaced the less accurate and less informative method of determining total water hardness solely by titration with standard soap solutions.
Reagents:
EDTA solution 0.02N (0.0lM)
Ammonia buffer solution
Sodium hydroxide solution 4N (4M) free form carbonate
Total hardness indicator tablets
Calcium hardness indicator tablets
Method
Total hardness
Transfer 100 ml of the sample, of between 10 and 200 parts per million hardness, to a white porcelain evaporating dish, add 2 ml of ammonia buffer solution and 1 total hardness indicator tablet. Titrate with EDTA solution 0.0lM until the solution in the dish has lost all traces of red colour. The final colour at the end-point is usually a clear blue, but with some waters neutral gray. If the hardness of the water is above 200 ppm in terms of calcium carbonate, a smaller sample should be taken.
Total hardness (ppm in terms of calcium carbonate) = titration in ml * 1000 / volume of sample in ml
Calcium hardness
Transfer 100 ml of the sample, of between 10 and 200 parts per million hardness, to a white porcelain evaporating dish, add 1 ml of sodium hydroxide solution 4M and 1 calcium hardness indicator tablet. Titrate with EDTA 0.0lM solution until the solution in the dish becomes violet. The endpoint is reached when the addition of 0.1 ml of EDTA 0.OlM produces no further colour change. If the calcium hardness of the water is above 200 ppm1a smaller sample should be taken.
Calcium hardness (ppm in terms of calcium carbonate) = titration in ml * 1000/volume of sample in ml
Magnesium hardness
The difference between the total hardness and the calcium hardness of the water is the magnesium hardness.
NALCO ANALYTICAL PROCEDURE
DISSOLVED CALCIUM HARDNESS
(Titrimetric)
(Includes tests for high and low level dissolved calcium.)
TEST KIT: Code C0033
RANGE: Unlimited
DETECTION LIMITS:
High Level Dissolved Calcium Test: 2 ppm as CaCO3 /0.1 mL of titrant
Low Level Dissolved Calcium Test: 0.1 ppm as CaCO3/0.l mL of titrant
PROCEDURE
High Level Dissolved Calcium
1. Use the l00-mL graduated cylinder to measure 50 mL of sample. Pour this sample into a 140-mL casserole (P0701).
2. Add 2 mL of H-6 solution (reagent S0279) to the sample and stir.
3. Add 2 or 3 shakes of H-7 powder (reagent S0280) and mix. The sample should turn pink.
4. Place the casserole under the burette with H-l solution (reagent S0274). Be sure the solution is at the zero level at the top of the burette scale. Open the valve and add the solution, one drop at a time, stirring gently until just one drop turns the solution purple. Close the valve.
5. Check the burette scale to determine the number of mL of H-l solution (reagent S0274) used.
CALCULATION
High Level Dissolved Calcium as ppm CaCO3 = (20)(mL of H-l used).
DISSOLVED CALCIUM HARDNESS (Titrimetric) HT-4
Low Level Dissolved Calcium
1. Use the l00-mL graduated cylinder to measure 100 mL of sample. Pour this sample into a 140-mL casserole (P0701).
2. Add 2 mL of H-6 solution (reagent S0279) to the sample and stir.
3. Add 2 or 3 shakes of H-7 indicator powder (reagent S0280) and mix.
a) If the sample turns purple, there is no dissolved calcium in the water and no need to continue the test.
b) If the sample turns pink, follow Steps 4-7 below.
4. Mix a control sample before your titrate. Measure 100 mL of sample water into another 140-mL casserole, add 2 mL of H-6 solution (reagent 50279) and stir. Add 2 or 3 shakes of H-7 powder (reagent S0280) and mix.
5. Place the test sample under the burette. Place the control sample next to it for colour comparison.
6. Fill the burette with LH-3 solution (reagent S0447 - not included in test kit). Be sure the solution is at the zero level at the top of the burette scale. Open the valve and add the solution one drop at a time, stirring gently, until the sample turns purple. Close the valve.
7. Check the burette scale to determine the number of mL of LH-3 solution (reagent S0447) used. Since 1 mL equals 1 ppm dissolved calcium, the number of mL used is the dissolved calcium reading in ppm as CaCO3.
NOTES
A Computerized Slug Injection System For Flow Measurement
Reference: G.W. Kite, 1989. An extension to the salt dilution method of measuring streamflow. Water Resources Development 5(1): 19-24.
Salt dilution provides an alternative to using a current meter to measure flows in fast mountain streams. The method has been used for many years but has been time-consuming and messy; necessitating the mixing of chemical solutions and the subsequent measurements of chemical concentrations. An method has been developed to use a laptop computer to control the conductivity measurements and to compute the streamflow directly in the field. The development of this method is described and examples are presented of the application of the method in the Rocky Mountains.
Flow data in mountain rivers are becoming increasingly important as recreation development occurs in high altitude regions. Mountain rivers are important sources of water for municipal supply, hydropower and irrigation. Knowledge of such flows is also vital in inter-jurisdictional disputes between upstream and downstream interests and for antic4pating the possible effects of climatic change and variation. The traditional velocity-area method of estimating flows is difficult and inaccurate because of velocity fluctuations and varying cross-sections.
The rapid turbulent flows that characterize mountain streams make them very suitable for dilution techniques of flow measurements. The basic principle of dilution gauging is the conservation of mass of some form of tracer. A known mass of tracer is introduced to the stream and its concentration is measured at some downstream point of the river. The tracer may be introduced as a continuous source or as an 'instantaneous' slug injection. Although other tracers such as radioactive isotopes, fluorescent dyes or microbiological agents may be used, the usual tracer is common salt, NaCl. The salt may be introduced in solution, as dry granules or even as salt blocks.
Because of the impracticality (and undesirability on environmental grounds) of introducing large masses of salt to the river, the dilution technique of gauging is only practical for flows less than about 15 m /s (Church, 1973). However, by taking advantage of natural salt sources in tributary rivers, the method can be extended to measure the flows of much larger rivers (Kite, 1989).
Until recently, dilution gauging has been cumbersome and time-consuming; needing accurate chemical glassware and analysis techniques in the field. However, since the introduction of compact conductivity meters and laptop computers the method is now quick and easy to use. This paper describes the development of a computerized dilution measurement system and its application in the Rocky Mountains of Alberta and British Columbia.