Figure 1 shows a vertical cross section through a typical concrete gravity dam with a cut-off trench two key requirements of this kind of a construction are: 1. controlled seepage flow beneath the dam 2. safety against dam failure -gravity dams depend on their mass for stability. they can fail by either sliding or overturning about the toe if the lateral pressures on the upstream become excessive the probability of either type of failure is increased by uplift pressures on the bottom of the dam, especially near the upstream face. therefore, uplift pressures must be known for the designs of safe dams you have been consulted to determine the flow rate of water under the dam and to calculate the uplift pressure at the bottom of the dam. the tasks you need to complete in order to do this are: task a: (i) construct a flow net on figure 1 showing groundwater flow under the dam (4 marks) (ii) calculate how much water is lost under the dam (the dam is 100 m long, soil hydraulic conductivity is 4 x 103 m/s, and reservoir depth is constant at 12 m with a tail water depth of 2 m) (2 marks) (iii) calculate the uplift pressure at point a on figure 1 (2 marks) task b:

Directions you probably already know that people have different ways to organize their ideas. some people make lists or outlines, some draw pictures, while others may combine these two methods. experiment with different note-taking techniques to find the one which works best for you. one common note-taking technique is webbing. webbing uses the sizes of circles to indicate the importance of items. lines are used to indicate the relationships between items. the example below is based on the information presented in a previous lesson. notice that the circle for "geography is" appears at the center of the web. it has larger than the circles that surround it. the "geography " circle is surrounded by smaller circles of earth's atmosphere, earth's climate, earth's surface. notice the lines that connect these items to the concept of geography. notice that the circles surrounding atmosphere are smaller. also observe that the lines that connect the items and indicate the relationships between the items. webbing will you capture the most important points in your lessons. beginning with lesson two, geographic tools: globes and maps, use webbing to take notes on the important information in this unit. hint: it will be easier to complete this project if you take your notes after completing each lesson.