River VL1 Flashcards
River def.
Any natural stream of water that flows in a channel with defined banks (Ufern).
- large body of fresh, flowing water
- flows in channel with defined banks
- ‘stream’
- importat natural terraformer, forming environment
- crucial ecological functions -> closely realted to terrestrial ecosystems
- significant to humankind
- concept of channeled surface flow
What is a helathy river?
A healthy river is defined by its intertwined physical, chemical and biological properties nad its connectivity along three key axes.
* longitudinal (flowing freely from its headwaters to its mouth),
* lateral (interacting with its floodplain and riparian zone), and
* vertical (allowing for movement of water, sediment, and organisms between surface and
subsurface habitats).
3 main axes of a river
- Upstream/ downstream
- Channel/margins
- Surficial/underground
margins- Randbereiche
RFI
River fragmentation Index:
how many rivers are impacted by dams (anthropogenic interference)
Indicators for and threats to helathiness
Healthiness: Clean water, rich biodiversity, natural flow patterns, and sustainable use.
Indicators: high diversity of macroinvertebrates and fish.
Threats: pollution, habitat destruction, over-extraction, and climate change.
What is the “Horton Overland Flow”?
It describes the flow of water over the Earth’s surface that occurs when the soil is unable to absorb all the precipitation water.
This typically occurs in areas with sealed surfaces such as asphalt or concrete, or when the soil is already saturated or has a low infiltration rate. Horton overland flow can lead to surface runoff such as erosion, flooding, and streams.
With which formula can the streamflow/discharge (Durchfluss = Q) be calculated?
Q = A * v
* (Q = m³/s)
- Width * Length -> Area (A)
- Area (m²) * Velocity of water (m/s) -> Discharge/Streamflow (Q = m³/s)
Since the current bed is irregularly shaped, it is divided into segments for better accuracy and the current flow for each segment is calculated and ultimately summarized.
What is the difference between perennial (mehrjährig) streams and intermittent (wechselnd) streams
and what are the reasons for that?
- Perennial streams are sustained by high and consistent groundwater supplies. This maintains the streams baseflow throughout the year, even during dry periods.
- Intermittent streams cease during dry periods, mainly due to low groundwater. The stream recharges the groundwater. This is typical for arid regions.
Flow metrics: 7Q10 and 7Q2; What is meant by that?
7Q10:
* Refers to the lowest 7-day average flow that typically occurs once every 10 years.
* calculated by examining flow data over a long period, usually from April 1 through March 31,
* identifying the lowest 7-day average flow observed during that time frame.
* This metric helps water managers understand the frequency and severity of low-flow events, which is essential for planning water resource management strategies and ensuring sufficient water supply for various uses.
7Q2:
* Similarly, this metric represents the lowest 7-day flow occurring over only two years.
* By focusing on a two-year period, it provides insight into more frequent but potentially less severe lowflow
events.
These metrics serve as standardized tools for evaluating low-flow conditions in rivers.
What is meant by “Q.50, Q.0.5, Q.0.95”?
What can be done with these metrics?
These are flow metrics used to understand the flow of a river and can be used to compare the flow (unit = m³/s) of two different streams, if the flow metric gets divided by the drainage area of the same stream (= normalization of flow to drainage area).
* (Just comparing the flow (m³/s) without
considering the drainage area is not accurate and can be misleading.)
* The drainage area includes all the land that contributes water to the river, including tributaries, smaller streams, and any surface runoff.
Q.50: Median flow of a river, meaning that 50% of the time, the flow is above this value,and 50% of the time, it is below. It provides a central measure of flow, helping to understand the typical flow conditions of the river.
Q.0.5: The flow that is exceeded only 5% of the time.This means that this high flow level occurs relatively infrequently. Is a useful metric for identifying the frequency of high-flow events, which can be critical for flood risk management and infrastructure planning.
Q.0.95: The flow that is exceeded 95% of the time. In other words, this is a low flow level that is quite common. Helps in understanding the typical low flow conditions, which are important for maintaining aquatic habitats and water quality during dry periods.
How do “discharge, oxygen-level, flow-velocity and annual mean temperature of the river” behave, when
examining a river from its upper reaches all the way to its lower reaches / its estuary (Mündung)?
While examining a river from its upper reaches downwards:
* the discharge (m³/s) and the annual mean temperature of the river increase,
* the oxygen-level and the flow-velocity are
decreasing.
Explain the main differences between bedrock, alluvial and mixed bedrock-alluvial rivers.
Definition and where do they mainly occur?
1) Bedrock Rivers
Definition: Rivers that flow directly over bedrock or through thin layers of sediment that do not significantly affect the river’s morphology.
Characteristics: Typically have steep gradients and
Occurrence: They are often found in mountainous or hilly regions (upland) and tectonically active areas where erosion has exposed the underlying rock.
2) Alluvial Rivers
Definition: Rivers that flow through loose sediments such as sand, silt, clay, or gravel, which
are deposited by the river itself.
Characteristics: Often have meandering channels and floodplains, with a dynamic and
changeable course.
Occurrence: Predominantly found in lowland areas, floodplains, and valleys where sediment
deposition exceeds erosion.
3) Mixed Bedrock-Alluvial Rivers
Definition: Rivers that exhibit characteristics of both bedrock and alluvial rivers, with sections
flowing over bedrock and others through alluvial deposits.
Characteristics: Show a combination of steep, bedrock-controlled segments and flatter,
sediment-controlled segments.
Occurrence: Often found in transitional areas where uplands meet lowlands, or in regions with
variable geology and sediment supply.
What is a transport limited, detachment limited and supply limited river?
Which of these terms suit alluvial and bedrock rivers?
Transport Limited River
* Definition: A river where the amount of sediment available for transport exceeds the river’s capacity to carry it. In other words, the river is limited by its ability to move sediment, not by the availability of sediment.
* Suitability: Typically, this term suits alluvial rivers, where abundant sediment is available, and the
river’s transport capacity determines sediment movement.
Detachment Limited River
* Definition: A river where the rate of erosion or detachment of sediment from the bed and banks is the limiting factor. The river’s ability to transport sediment is greater than the rate at which it can
erode and detach material.
* Suitability: Can occur in both bedrock and alluvial rivers. In bedrock rivers, the bedrock itself is hard to erode. In alluvial rivers, it can occur when the river encounters resistant materials like consolidated clay or glacial till.
* Focus: Erosion Process
Supply Limited River
* Definition: A river where the sediment supply is restricted due to limited sources of sediment. The river’s transport capacity exceeds the amount of sediment available for transport.
* Suitability: This term applies to bedrock rivers, where the availability of loose sediment is limited, restricting the overall sediment supply.
* Focus: Sediment Availability
Summary
* Alluvial Rivers: Best described as transport limited, since they often have an abundant supply of sediment.
* Bedrock Rivers: Best described as supply limited, due to the limited availability of loose sediment. (Detachment limited focusing on the erosion stage and supply limited focusing on the availability of already eroded material).
1) What is an “oxbow lake”?
2) What are the features of “pools, riles and runs” in a river?
1) An oxbow lake (Altwassersee) is formed when a meander is cut off from a rivers mainstream.
2) Pools are deeper locations in a river bed where the water flows slower, whereas riffles are fastflowing shallow areas. Runs are areas of a river or stream where the water flows smoothly and steadily, with a relatively uniform floor. They are typically located between pools and riffles and
connect them.
What is a floodplain? Which two major processes are involved in the natural development of
floodplains? What do they do?
A floodplain is a flat area of land adjacent to a river that is subject to periodic flooding and built up by
the deposition of sediment over time.
* Erosion: Removes material from the river channel and banks, reshaping the landscpae
* Aggradation: Deposits sediment, building up the floodplain over time.
