WETTED PERIMETER CROSS SECTIONAL AREA HYDRAULIC RADIUS The efficiency of the channel Cross sectional area --------------------------- Wetted perimater Width x 2 (depth) The total length of the bed and bank sides that comes into contact with water in the channel The amount of water in the wetted perimeter of the channel Width x mean depth of the channel
ROUGHNESS COEFFICIENT (MANNINGS ‘N’) VELOCITY DISCHARGE The rate at which water moves through the channel V = R (0.67) x S (0.5) ---------------------- n Cross-sectional area X Velocity The speed of the water in the channel The frictional force of a river bed and its effect on velocity Discharge -------------- Cross sectional area
Primary Research—The data for investigation must come from the student’s own personal observations and measurements, that is, it should be collected in the field. This “primary data” should form the basis of each investigation. Fieldwork should provide sufficient data to enable adequate analysis and interpretation.
Secondary Research—Secondary research involves gathering data from sources that have already been compiled in written, statistical or mapped forms. It would include data from a population census and meteorological offices. Data collection in the field may not supply all the information required for some investigations and therefore the inclusion of some “secondary data” is important. However, too much secondary data should be avoided as should descriptive investigations that rely heavily upon observation without measurement.
Students should produce one written report of 2,500 words of their investigation. Maps, diagrams, graphs, statistical analyses and other supplementary information (such as the title and contents page and references) are not included in the word limit.
The aim (aims) is neither realistic nor clearly focused. There is a hypothesis (hypotheses) but this is not justified. The locational context and theoretical background provided are limited.
The aim (aims) is focused and there is an appropriate hypothesis (hypotheses) with justification. The locational context and theoretical background provided are sound, but the treatment of one may be better than the other.
The aim (aims) is well focused and there is an appropriate hypothesis (hypotheses) with justification. The locational context and theoretical background are strong and there is a clear link between them.
There is only a brief statement of the methods used for the data collection and these may be inappropriate to the research. As a result there is very little data and it is generally of an inappropriate type or of poor quality. Very limited knowledge of sampling techniques is evident.
There is an adequate description of methods used for the data collection and they are appropriate to the research. As a result there is an adequate amount of primary data. Where relevant, some knowledge of sampling techniques is evident.
There is a clear description and justification of the methods used for data collection. The methods used are appropriate and accurate, sometimes inspired (something original not ordinary) and produce data of high quality. Where relevant, a good knowledge of sampling techniques is evident.
0 There is no evidence of appropriate data presentation or data processing.
The presentation of data is poor. Illustrations and written text are inadequate. There is an absence of maps or, where these are included, they are limited and reveal a narrow range of mapping skills. The use of graphical techniques is limited. Statistical techniques to process data may be missing or, where they are used, they are either applied out of context or calculated inaccurately. There is a heavy dependence on secondary data.
The presentation of data, illustrations and written text is adequate. Maps are included and demonstrate some variety of skills. An appropriate, if limited, range of graphical techniques is used. Statistical techniques to process data are used and there is some understanding of their significance.
The presentation of data, illustrations and written text is good. Maps are included and demonstrate a good variety of mapping skills. There is a wide range of relevant and sometimes imaginative graphical techniques. There is a competent and thorough use of statistical techniques and, where appropriate, tests of significance.
0 There is no reference to the aim (aims) and hypothesis (hypotheses) and no discussion.
The description of the findings is very brief with little discussion and with little reference to the aim (aims), the hypothesis (hypotheses) and theory. The report reveals that there is generally little depth of understanding.
There is an attempt to provide an adequate reference to the aim (aims), the hypothesis (hypotheses) and theory. The description of the findings presents a simplistic argument either accepting or rejecting the hypothesis (hypotheses). The report reveals that there is a limited depth of understanding. There is some reference to maps and illustrations.
There is a reasonable attempt to refer to the aim (aims), the hypothesis (hypotheses) and theory. The description of the findings presents a sound argument either accepting or rejecting the hypothesis (hypotheses). The report reveals that there is some depth of understanding in the discussion. Attempts are made to explain anomalies in results. There are references to all maps and illustrations used.
There is a good attempt to refer to the aim (aims), the hypothesis (hypotheses) and
theory. The description of the findings presents a reasoned and balanced argument either accepting or rejecting the hypothesis (hypotheses). The report reveals a depth of understanding in discussion. Attempts to explain anomalies in results are good. There are clear references to all maps and illustrations used.
There is a very clear interpretation of the results with strong references to the aim (aims), the hypothesis (hypotheses) and theory. The description of the findings presents a well reasoned, balanced and critical argument either accepting or rejecting the hypothesis (hypotheses). The report reveals a good level of understanding and the discussion is sophisticated and detailed. Attempts to explain anomalies in results are very good. There
are very clear references to all maps and illustrations used.
The conclusion is very basic, or inconsistent with the data presented in the report. There may be attempts to provide a summary of results. There is some attempt to evaluate the methods of data collection and processing. There are no recommendations for improvements or extensions.
The conclusion is adequate and some attempt has been made to evaluate the methods of data collection and processing. There are brief recommendations for improvements or extensions.
The conclusion is sound and consistent with the data presented in the report. Methods of data collection and processing have been evaluated clearly. There are some good and sometimes imaginative recommendations for improvements or extensions. There may be some suggestions for modifying the hypothesis (hypotheses).
An investigation into how channel parameters change from source to mouth River Holford
The source of the River Holford (Lady’s Fountain) is in the Quantock Hills (Robin Uprights Hill at 300m)
The river Holford flows north for approximately 8km
The mouth of the River Holford is at Kilve Beach. It enters the Bristol Channel.
The drainage basin is steep sided and wooded in its upper course
The river Holford flows over three distinctive geology types.
Devonian quartzite in the upper course (Sites 1-6),
(Quartzite is an impermeable rock that is very resistant)
Marl in the middle course (Site 7)
Marl is a soft sedimentary rock with a high clay content. It is also impermeable
Limestone in its lower course (Site 8).
Limestone is a permeable sedimentary rock – harder than marl but softer than quartzite
There are two settlements along the course of the river. These are Holford (between Sites 6 & 7) and Kilve (between Sites 7 & 8). Human influences on the river include altering the channel, polluting river, water extraction and water treatment
Width increases because … increased discharge causes increase in energy which increases erosion so widening the river
Depth increases because … increases in volume mean and increase in energy. This results in as increase in vertical erosion so the channel is deepened
Velocity increases because … increased volume of water so increased hydraulic radius. This results in increased efficiency and a decrease in friction so less energy is lost
Discharge increases because … more water will have the chance to enter the main channel from tributaries and groundwater stores. It is also influenced by the increase in velocity.
Roughness decreases because … increase in volume of water means an increase in hydraulic radius so the channel becomes smoother. An increase in velocity also contributes to this process. Attrition and abrasion reduce the size and angularity of the bed load
Slope angle decreases because … the addition of water through tributaries, throughflow, surface-runoff etc. leads to increased hydraulic radius. This results in less erosion of the bed and banks.
Sediment size decreases because … increased velocity increases the level of erosion, especially attrition which leads to sediment becoming rounder and smaller
The choice of sites sampled was greatly influenced by landuse. Between Sites 1 and 6 relatively even sampling was possible as accessibility was not a problem. In the middle and lower course more restrictions were in place as areas close to the river were taken up by private settlements (back gardens) and private farmland
It was important to sample a large number of sites in the upper course as the river characteristics under investigation are more marked in this region (i.e. they happen quicker).
It was also important to collect data from all three rock types as geology may impact upon the characteristics of the river itself.
Finally, the number of sites sampled was influenced by time limitations .
All of the data collected is primary and quantitative (except sediment angularity which is qualitative)
2 groups collected the data over a 10 metre stretch of river at each site. The results were combined and then averaged out.
For channel width a tape measure was used. Statistics were recorded in metres.
For channel depth a metre rule and a tape measure were used. The depth was measured at 6 points across the channel. These points were at regular intervals.
For wetted perimeter a tape measure was used.
For velocity a stop watch, hydroprop and impellor were used. The velocity was measured at 4 points across the channel.
For sediment size a pebblometer was used to measure the a-axis. 5 samples were chosen at approximately equal intervals across the channel.
For sediment angularity, Power’s Roundness Index was used. The samples chosen were the same as those used to assess sediment size. Although Power’s Roundness Index is not directly linked to Bradshaw’s Model it helps explain results)
For channel gradient a theodolite (dumpy level), tripod and measuring staff were used. The gradient was assessed over a 10 metre downstream stretch of the river.
The choice of sites was stratified . In other word, samples were taken from each of the three rock types. The choice of sites was not systematic . In other words, samples were not taken at regular intervals along the course of the river. This was due to limitations in accessibility along with health and safety issues.
The depth and velocity measurements were systematic as they were taken at regular intervals across the channel.
The choice of clasts was systematic as they were taken at regular intervals across the channel. However there was a choice of clasts at each point and so the actual clast surveyed was chosen at random.
The scattergraph shows that velocity generally increases downstream
There was an increase at site 2 due to confluence
At site 3 there was a slight reduction in velocity which may be due to braiding in the channel, variable flow, wider channel at this point, less water
There was an increase at site 4 after the confluence
At site 5 and 6 there was little change which could be due to human influence and the mill pond
At site 7 velocity was seen to rapidly increase due to the tributary from Hodders Coombe and also the change in underlying geology to a softer marl. This enabled the river to alter its gradient and vertical erosion to become more dominant – with the effect that velocity increases.
At site 8 there was a slight decrease. Once again there has been a change in underlying geology but there is also the added factor of human influence. The topography of the area is flat