Consider the case that due to climate changes, the existing design of the reserv
ID: 298537 • Letter: C
Question
Consider the case that due to climate changes, the existing design of the reservoir and the pipe system in an urban and residential area within a watershed (see Figure 1 below) can no longer handle the floods or sustain the droughts. Impacts of the climate changes on the watershed in this case is manifested in having higher frequency of larger rainfall events (flooding) as well as a longer period of a dry season (drought). In other words, although the mean annual precipitation amount over multiple years may remain the same, higher intensity rainfalls have now occurred more often, and at the same time no-rain periods are also prolonged. For the given site, the reservoir is located in the upstream portion of the watershed while the pipe system is located in the lower portion and close to the watershed outlet. Please answer the following questions. If you need to make any assumptions, please clearly state them.
(5) Describe how you want to modify the existing design to mitigate the impacts of the described climate changes (provide general plan for both upstream area and the pipe system downstream).
Figure 1. The watershed of your study area which has a drainage area of 100 kmExplanation / Answer
5. Road drainage design should be such that it minimises the energy of flowing water because the destructive power of flowing water increases exponentially with increase in its flow velocity. Many of the drainage problems like erosion of the road surfaces can be avoided with proper drainage design. The stability of a road depends upon factors like slope morphology and other hydraulic factors. Some of the important factors like shape of slope, slope gradient, length of slope, drainage pattern of stream eg. braided, dendritic, depth to bedrock and other characteristics of bedrock like bedding, hardness, fractures, texture of soil and permeability etc. Convex slope will tend to disperse water as it moves downhill, straight slopes will concentrate water on the lower slope and concave slopes will result in concentration of water in its lowest point. Thus concave slopes is the most undesirable locations for the road design.
In general the roads built on the upper one third part of slope are stable because of better soil conditions whereas roads built on lower positions will be unstable. Also care must be taken that the natural drainage characteristics of slope should not be modified because if modified it will cause excessive erosion of soils and thus further decrease its stability. Also the design should be such that it dissipates water away from the roadway and prevents collection of excessive water in the unstable areas and reduces downstream erosion.