Streams and Floods Flashcards
Define stream load and explain what factors control it
Stream load: materials that are carried and transported by a stream or river. Consists of dissolved load (ions dissolved in the water), suspended load (particles carried in suspension), and bed load (particles moved along the streambed). Factors: stream velocity, volume of water flowing, the size and density of the particles, slop of stream channel
Why do stream sediments tend to be well sorted?
Stream sediments tend to be well sorted because the sorting process occurs as a result of the varying velocities of water within the stream. Faster-moving water can transport larger and heavier particles, while slower-moving water can only transport smaller and lighter particles. This differential transport leads to the sorting of sediment particles by size, resulting in well-sorted sediments.
Explain how migration and enlargement of meanders contributes to floodplain development.
Meander migration and enlargement contribute to floodplain development by altering the shape and size of the river channel. As meanders migrate laterally and enlarge over time, they erode the outer banks and deposit sediment on the inner banks, creating a wider and flatter floodplain. This process increases the capacity of the river to accommodate floodwaters and reduces the risk of flooding in surrounding areas.
Describe some of the factors that cause rivers to be braided, rather than meandering.
Rivers become braided rather than meandering due to high sediment supply, variable discharge, and a steep channel gradient. When a river has more sediment than it can transport, it deposits excess sediment, creating bars and islands within the channel. Variable discharge, caused by factors like seasonal rainfall or glacial meltwater, can lead to fluctuations in channel capacity, promoting the formation of multiple channels. Steep channel gradients can also encourage braiding by increasing the energy available for sediment transport.
What is a flood-frequency curve?
A flood-frequency curve is a graph that illustrates the relationship between the magnitude of floods and their frequency of occurrence. It plots the discharge or stage of a river against the probability of exceedance (chance of a flood of a certain magnitude occurring in a given year). This curve is essential for assessing flood risk and designing flood control measures.
What is recurrence interval and how is it determined?
The recurrence interval is the average time interval between floods of a particular magnitude or greater. It is determined by analyzing historical flood data and constructing a flood-frequency curve. The recurrence interval can be calculated using the formula: Recurrence Interval = (N + 1) / M, where N is the number of years of record and M is the rank of the flood event.
Describe how urbanization can affect stream flooding.
Urbanization can affect stream flooding by increasing the amount of impervious surfaces such as roads, buildings, and parking lots. These surfaces prevent water from infiltrating into the ground, leading to rapid runoff during rainfall events. As a result, urban areas experience higher peak flows and more frequent flooding.
