topographic map, this abrupt slope increase occurs where the contour lines become closely spaced. For example, the purple lines on the topographic map in Figure 6.4 coincide with the upper edge of the floodplain where the slope abruptly increases. Note that due to erosion, this change in slope is oftentimes more gradual and, therefore, not as obvious on a map.4) Using a purple-colored pencil or marker, carefully trace the edge of the floodplain along the north-south flowing stream on the eastern side of the map in Figure 6.4. Note that part of the floodplain has already been mapped for you.5) Are there any buildings or roads within the floodplain? Explain why.There are no buildings or roads within the floodplain because the probability of having property orvehicle damage is evitable in high risk flood zones especially on the valley floor. A floodplainrepresents the base level of all water flow. So, because of the greater amount of water volume inthat flat surface, any building or road in its path will unundate the area. This could leave buildingsor roads underwater for a long period of time.6) In Figure 6.4, part of the drainage divide on the south side of the tributary named Big Branchhas already been mapped for you. Continue tracing this drainage divide (in red) until you come to the southern most edge of the map.54Ex 6 – Streams and Flooding
Ex 6 -Streams and Flooding
7) The drainage divide you mapped in Figure 6.4 follows the high ground that is left behind when streams naturally etch, or cut, into the landscape. Describe the general relationship between drainage divides and human uses of the landscape that you see on the map (e.g., buildings and roads).