Final answer:
Approaching a low-head dam is hazardous due to dangerous currents, potential for dam failure, and ecological impacts. Dams can create unstable conditions, and history has shown that disasters involving dams, like the Vajont Dam incident, can lead to catastrophic consequences.
Step-by-step explanation:
It is hazardous to approach a low-head dam due to several factors. Firstly, low-head dams can create deceptively dangerous currents and backwash that can trap objects and living creatures, posing a significant risk to anyone who enters the water near them. Additionally, the water pressure and force exerted against a dam, as indicated in FIGURE 11.9 and 11.14 of the provided reference material, show that even though this force is small compared to the weight of the water retained, it is sufficient enough to cause stability concerns. When there is significant water flow, such as during flooding or high-rainfall periods, the force exerted can be unexpectedly hazardous, potentially leading to dam failure and downstream flooding.
Moreover, dams can affect local ecology and the environment. They can change natural water habitats, affecting the river's chemistry, flow, silt loads, and water temperatures. This can lead to significant shifts in the river's ecology both upstream and downstream. In cases like the Vajont Dam disaster, poor site selection, and geological instability can lead to catastrophic outcomes, as it did in 1963 when a landslide caused the dam to overflow, resulting in the loss of nearly 2,000 lives.
Therefore, due to these potential risks and the historic consequences observed with dam-related disasters, it is why approaching a low-head dam is considered hazardous.