Water contour line definition8/8/2023 This method is slow and tedious and thus used for large scale maps, small contour interval and at high degree of precision. Points which happen to fall on a desired contour are only surveyed, plotted and finally joined to obtain the particular contour. In the direct method, the contour to be plotted is actually traced on the ground. In general, the field methods of contouring may be divided into two classes: Thus, contouring depends upon the instruments used (to determine the horizontal as well as vertical position of points). Contouring involves providing of vertical control for location of points on the contours and horizontal control for planimetric plotting of points. It requires planimetric position of the points and drawing of contours from elevations of the plotted points. The method of establishing / plotting contours in a plan or map is known as contouring. The process of locating these contour lines on the surface of the earth is known as contouring. It should be remembered that the contour interval for a particular map is constant. and for large scale map,it may be of 0.25m,0.50m,0.75m etc. 5m, 10m, 15 m etc.Īgain ,for a small-scale map, the interval may be of 1m,2m,3m etc. For a steep slope in hilly area is greater, eg. This interval depends upon,Ĭontour intervals for flat country are generally small, eg. For example, if the various consecutive contours are 100m, 98m,96 m etc., then the contour interval is 2m. The vertical distance between any two consecutive contours is known as a contour interval. The concavity in contour lines is towards higher ground in the case of ridge and towards lower ground in the case of valley . Contour lines in U-shape cross a ridge and in V-shape cross a valley at right angles. A set of ring contours with higher values inside, depicts a hill whereas the lower value inside, depicts a depression (without an outlet).Ĭontours deflect uphill at valley lines and downhill at ridge lines. They are perpendicular to ridge and valley lines where they cross such lines.Ĭontours do not pass through permanent structures such as buildings.Ĭontours of different elevations cannot cross each other (caves and overhanging cliffs are the exceptions).Ĭontours of different elevations cannot unite to form one contour (vertical cliff is an exception).Ĭontour lines cannot begin or end on the plan.Ī contour line must close itself but need not be necessarily within the limits of the map.Ī closed contour line on a map represents either depression or hill . The steepest slope of terrain at any point on a contour is represented along the normal of the contour at that point. Thus, contours are spaced equally for uniform slope The horizontal distance between any two contour lines indicates the amount of slope and varies inversely on the amount of slope. The variation of vertical distance between any two contour lines is assumed to be uniform. The principal characteristics of contour lines which help in plotting or reading a contour map are as follows: It facilitates depiction of the relief of terrain in a two dimensional plan or map. The path that water takes in the aquifer, defined as a continuous line tracing the maximum gradient on a map of the potentiometric surface, is known as a flowline.A line joining points of equal elevations is called a contour line. In two dimensions, the head gradient is defined by the slope of the potentiometric surface – just as the slope of the land surface is defined on a topographic map. In a simple one-dimensional Darcy tube experiment, the head gradient is just the difference (h1-h2)/L. the hydraulic gradient) and hydraulic conductivity. If you think back to Darcy material and our in-class activity from last week, you will recall that groundwater flow rate depends on the head gradient (i.e. The potentiometric map also provides clues about the rate of groundwater flow. There are exceptions to this – for example, if the hydraulic conductivity of the aquifer is much higher in one direction than another, or dominated by fractures with particular orientations, then these can redirect groundwater flow askew to the maximum gradient. As is the case with surface water, or a ball rolling down a hill, the water flows in the direction of the steepest gradient, meaning that it flows perpendicular to equipotentials. To first approximation, groundwater flows down-gradient (from high to low hydraulic head). Each contour, or equipotential, represents a line of equal hydraulic head. These maps define the potentiometric surface, which is much like a topographic contour map but defines the distribution of potential energy in the groundwater system. In order to define groundwater flow directions and rates through aquifers, individual measurements of hydraulic head are combined to generate contour maps of water level – or potential energy (Figure 29). Hydraulic Head and the Direction of Groundwater Flow
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