Map Work: Mendips This exercise consists of the five questions detailed in the following sections. The five questions refer to Cheddar Gorge and Blagdon reservoir, both in the Mendips area. The maps you use in this exercise are sourced from Digimap. Question 1.1: Cheddar Gorge map - Scale of map For this question, you must use the Cheddar Gorge map available on BlackBoard. You can either print it or work with the electronic version. If you work with the electronic version, make sure the map is displayed at its actual size (100%). a) Calculate the scale of the map using the scale bar. b) Determine the distance between the two points A and B (note: the location is the centre of the X, not the letter). To calculate the scale, you will need a ruler to measure the distance between those two points on either the map printed or your screen. The scale has to be calculated in two forms: • An equivalence relation: e.g. 1cm= x km • A ratio: e.g. 1: X000 Question 1.2: Cross sectional form of Cheddar Gorge For this question, you must use the graphic paper available on BlackBoard or handed out during the session. Using the graphic paper, draw the topographic cross sections between the points A and B shown in in yellow in the Cheddar Gorge map available on BlackBoard. The section should be finished with the following: a title, labels for the start and finish point, horizontal and vertical scales, factor of exaggeration and the orientation (compass directions). The videos available on BlackBoard as well as the guidance notes at the end of this document will help you. Question 1.3: Blagdon reservoir watershed map You are required to either use Digimap or the Blagdon map provided on Blackboard to answer this question. A link to Digimap is available on BlackBoard. a) Draw in the watershed of the River Yeo upstream of the reservoir. You have to ensure you delineate between adjacent rivers and catchments, but you must also use the contours to ensure your watershed is always on the highest ground. b) Now consider the following scenario: an accident happened on the main road midway between Compton Martin and West Harptree near the turn off to Beaconfield and involved a fuel truck. What is you suggestion, would you monitor water quality at Bladon reservoir or at Chew Valley lake? Explain your answer. The videos and document available on BlackBoard as well as the guidance notes at the end of this document will help you. Guidance on the Map Work Exercise Guidance on drawing topographic cross sections 1. Identify the start and finish points for the first section and draw on the map the line of section. 2. Put a piece of plain white paper along the line of section and mark every contour that is crossed with the associated heights of the contour lines. The contours occur in 5 m intervals on this map and therefore if you cannot find a height value on the contour, you can work out its value by counting up or down from adjacent contours. The bold contours mark the 25s, 50s, 75s and 100s of metre levels. Where there are no contours, look for spot heights as a guide to height above sea level (also known as height above Ordnance Datum abbreviated as OD). 3. Transfer the data to the 3G graph paper (available on BlackBoard). a. Draw a line (the section line) the length of the section across the graph, which should be in portrait format. b. Draw vertical lines of 10 cm up at either end of the section line. Mark heights on these lines with a reasonable vertical scale considering the minimum and maximum elevation occurring along your cross section. Because of the altitude of this landscape it is acceptable to start the vertical scale at a point just below the lowest contour on your section - you must determine this. c. Draw on the graph paper a cross for each intersection of the line of section with a contour line, its coordinates being the distance between the intersection and the start point and the height of the contour line. 4. Join all of the crosses with a smooth line. 5. To complete the section, mark on the horizontal and vertical scales, an appropriate title, compass directions, names of the locations and features such as roads, footpaths, quarries, etc. and the end and start point of your cross section. Guidelines on determining the position of a drainage basin (catchment) watershed Geomorphologists and hydrologists often view streams as being part of drainage basins. A drainage basin is the topographic region from which a stream receives runoff, throughflow, and groundwater flow. Drainage basins are divided from each other by topographic barriers called a watershed or water divide. A watershed represents the boundaries of the area where all of the stream tributaries flow to some location along the stream channel. The number, size, and shape of the drainage basins found in an area varies with the scale of examination. Drainage basins are arbitrarily defined based on the topographic information available