Lecture 8/9: Surfacewater + Groundwater Flashcards
Describe different types of surface water flow
stagnant (buffer)/river flow (water draining into it > flowing out)
Surface waters receive input from:
- Precipitation
Overland flow
o If the soil is saturated and can’t absorb water fast enough. If precipitation runs off the surface
Throughflow
o Easier for water to flow horizontally: if the propensity for water to flow through is higher horizontally than vertically, the water is going to flow through the soil as throughflow.
Baseflow
o Groundwater that pushes its way back into the rivers (by pressure)
What’s the difference between quickflow and baseflow?
Baseflow is over a longer period of time, while quickflow is very quick. Baseflow is made up from groundwaterflow. Quickflow is made up from overland flow, precipitation into surface water and throughflow.
What influences overland flow?
Steepness of the terrain, soil type, Dikes/built-up areas and saturation (fills up the soil to the point where it can’t take anymore water)
What is baseflow and why is it important in large rivers?
streamflow or river discharge that comes from the slow release of water from underground aquifers, such as groundwater, rather than from surface runoff
When water infiltrates into the soil most will percolate into groundwater. This is slowly moving water and decreases after long periods of drought.
It’s important because it feeds rivers in dry periods
What determines river flow?
velocity, hydraulic cross section, gradient, channel roughness (how much resistance does the riverbed provide).
What are the differences between higher and lower areas in NL from a hydrological pov?
Higher areas:
- erosion: potential energy in water. Gravity pulls it down.
- pick up material and transport it downstream
- water is lower lying than surrounding areas
- transport by gravity
Lower areas:
- lower lying than main water channel
- transport by pumping stations
- sedimentation: eroded material that’s picked up earlier, higher up –> flow slows down, drop in gradient, energy lessens –> sedimentation.
Explain water quality briefly
Chemical characteristics of dissolved material. Is dependent on physical characteristics of the water like temperature, taste and suspended soils.
What is groundwater?
- 95% of the liquid fresh water is groundwater
- Water in pores between sand grains (25-40%)
- Water in ground beneath the uppermost layer soil where there are plant roots and air.
What is groundwater used for?
Drinking water
Industrial water
Agriculture
Shipping/rivers
important for groundwater dependent ecosystems
Differences in groundwater in low and high areas of the Netherlands?
High: pushed water out, groundwater tries to make its way up
Low: polder areas. water is controlled by pumping. Water is pushing its way up in poldered area, because you have higher lying areas that push the water down and then it comes back up.
What is a consequence of seepage in the lower parts of the Netherlands?
Higher groundwaterstance. It would constantly be wet.- This is why we are pumping the polder lands.
Explain Darcys law
- Not every substrate is the same.
- Material that it flows through is gonna determine the resistance that the water is gonna experience.
o Sand: water is gonna flow through it easily.
o Chalk,granite, clay: much harder
Hydraulic conductivity determines how easily the water flows through. The higher this is, the easier it flows through. e.g. Hydraulic conductivity with sand is high.
How does salination happen?
Freshwater lands are smaller. Brackish/salt water pushes its way into the polder because the land is too low. Brackish seepage in between freshwater seepage.
What is the difference between soil water and groundwater?
Soil water: unsaturated zone above groundwater table
Groundwater: saturated zone including capillary fringe.
