NCWR

About NCWR

The water basins

In a nutshell

In this activity we learn about the water drainage basin and how it is linked to our activities.

60 minutes

12-13 years old

In class

Our objectives

In this activity you will:

  • Observe and identify the drainage basin of your area.
  • Explore the flows of water in a drainage basin.
  • Learn what “water balance” means.

Things to use

large pieces of paper, a big pan, a spray bottle, markers

Play & Learn

Tracking the drainage basin of my area!

Wherever you are on earth, if you step on land you are actually inside a “water catchment area” or “drainage basin”, meaning the area that drains the rainwater that is flowing on the land surface, as runoff and is collected in streams, channels, rivers or lakes. Take a look up, at the ridge  of the mountain (or hill) surrounding you: you are in the “bowl” of the side you see, while the backside of the mountain belongs to the adjacent drainage basin.

To understand how a drainage basin operates, observe the roof of the house below. When rain falls on the roof, how many directions can  the water follow?

Water-readings

What is a water (drainage) basin?

The drainage basin is an area surrounded by hills or mountains, in which all surface waters flow as runoff towards a river, a lake, or eventually to the sea due to gravity and inclination. Virtually every river is inside a drainage basin: the larger the basin, the more the water drained.

The figure above shows how the (red line) separates a drainage basin (red arrows) from the neighbouring ones (green arrows).

Why do hydrologists study the drainage basin around a city? Here are some reasons: 

  • They observe the water’s direction and estimate where it might be collected (e.g. in a dam) before escaping to the sea.
  • They identify locations that might be rich in groundwater -depending on the direction of the surface water. Of course, groundwater existence depends also on the underground rock composition.
  • They detect the pollution paths, in order words, how the pollutants are transported from any point of the basin towards the collection point.
  • They estimate the amounts of water that the basin receives () and whether this is sufficient for the surrounding settlements.
  • By knowing the water precipitation and direction inside the basin, they can design the necessary flood-prevention works to protect the surrounding settlements.

Stop and wonder

Discuss in your groups:


  •  In the area where you live, where does water come from?
  • Do you receive enough precipitation in your basin to cover the needs of the settlements and the cultivated lands (irrigation)?
  •  If water in your area comes from another basin, how far does it travel?
  •  Drainage basins have no national borders. Does your area’s basin belong exclusively to your country or is it shared with another country?

Contact an expert, e.g. form the local Water Agency that could answer these questions. 

Group activity

Let’s make the model of the water basin

  1. Crumple some sheets of newspaper or carton, making sure you create “mountains” and “valleys”.
  2. Lay your folded creation that looks like a watershed, inside a pan. Optionally you can colour its sides.
  3. Spray the “mountain tops” with water and observe how the water flows. When you finish steps 1-3, discuss the following.

Discussion Points


What do the following elements of your model represent in real life?

  • sprayed water
  • peaks on the folded paper
  • hollow surfaces of the paper
  • water flowing on the paper
  • water penetrating the paper
  • water accumulating at some spots
  • the entire model

Play & learn

What do the following elements of your model represent in real life? Drag and drop to find out!

A: Model

B: Parts of a water drainage basin

  • 1 the water from the spray 1
  • 2 the peaks on the crumpled paper 2
  • 3 the hollow surfaces on the paper 3
  • 4 the water flowing on the paper 4
  • 5 the water absorbed by the paper 5
  • 6 the water that accumulates in certain spots in the pan 6
  • 7 the entire model (pan-paper-water) 7
  • 1 rain
  • 2 watershed
  • 3 valleys
  • 4 water run-off (rivers, torrents, streams)
  • 5 groundwater
  • 6 lake or sea
  • 7 drainage basin

Water-readings

The water balance inside a drainage basin

When water enters a drainage basin (water inflow) through precipitation (rain and snow), a part of it may be retained in the basin e.g. in a lake, a wetland or as groundwater reservoirs, while the rest “escapes” through evaporation, transpiration and surface runoff (water outflow).

If we think this inflow and outflow of water as a balance, then the total inflow to an area must equal the total outflow plus the net change in storage.

The water balance studies:

  • The inflows: How much water precipitates into the basin every year and in which form e.g. rain, snow, hail.
  • The outflows: How much water flows each year from the basin mainly from the rivers that run off.
  • The storage: How much water is available in the basin, mainly found as groundwater or in dams and lakes.

Obviously, during the dry seasons the inflows (and storage) are decreasing. On the other hand, when storms occur, a substantial amount of inflow is lost to the sea, as it does not have time to percolate and enrich the  groundwater. Unfortunately, Climate Change accelerates both the draughts as well as the torrential downpours all around the planet, and we have to cope with that.

To properly manage the water of a basin, experts have to monitor systematically and over time its inflows and outflows, and take the necessary measures, in case that water resources are not sufficient to meet the needs of its settlements and agriculture activities.

Play & learn

Decide whether the following cases are considered as inflows or outflows.

Inflow Outflow
Melting snow

Melting water is an inflow for the basin!

Rainfall

Upstream of a river

The river is “adding” water to the basin, so it is an inflow.

Transpiration of plants

During transpiration, the absorbed by the roots groundwater, is led to the leaves and part of it evaporates. In this way, water from the basin decreases, so this is an example of outflow.

Evaporation in a lake

Due to evaporation the water of the lake decreases, thus it is example of outflow.

A river delta

Any river or stream ending up to the sea is an outflow for the basin.

Water-readings

Let’s become hydrologists…

Would you like to become an hydrologist? This is an expert who studies water, the hydrological cycle, the water inflows and outflows of the drainage basins.

As an a hydrologist, you can roughly calculate the inflow in the drainage basin of your area every time it rains, if you know:

  • the rainfall in millimetres (mm). You can measure the height of rain with a rain gauge. You can find instructions on how to make a rain gauge here and a short video tutorial here.
  • the surface of your catchment area. Here is an interesting online tool where you can draw an area on a map and find out its enclosed area.

Estimate, the water inflow into the basin, every time it rains, is:

Rainfall (mm) x area (m2) x 1000 = ....... (cubic meters)

Knowing that an Olympic pool (50m x 25m x 2m) is filled with 2,500 cubic meters of water, how many pools could be filled with the amount of water you calculated?

Water shares


Water meter

I liked this activity . . .

Way forward

Surfing around the Internet

Visit the website of your National Meteorological Service to find out about the average rainfall in your area/drainage basin.

Dive in …

Water in the city if you want to explore where water comes from in your city.

The water cycle in a bowl! if you want to learn more about the water cycle .

Go back to the homepage!

The water basins

Water in the city

Desalination

Do you know about grey water?

Rainwater harvesting

Greywater recycling in practice

Wastewater treatment

The water cycle in a bowl!

Waterworks through time

Climate change challenges

Rainwater Harvesting Systems in practice

Reduce-Reuse-Recycle

Water resources

Where do I begin?

The water basins

In this activity we learn what a water drainage basin is and why it is important for the experts to study it.

Continue!

Water in the city

What is the "urban water cycle"? Which are the important aspects of water management within a city environment?

Continue!

Desalination

Let's find out how sea and brackish water can become a freshwater resource!

Continue!

Do you know about grey water?

Let's find out what "greywater” is and how we can use it!

Continue!

Rainwater harvesting

Can do we collect rainwater? And how do we use it? Let's find out!

Continue!

Greywater recycling in practice

How a grewywater system is installed? Let's find out!

Continue!

Wastewater treatment

In this activity we learn about how wastewater is treated and what we can do with the treated water.

Continue!

The water cycle in a bowl!

Let's travel within the water cycle!

Continue!

Waterworks through time

Let's discover the story behind the historic fountains, cisterns and aqueducts of our town!

Continue!

Climate change challenges

Time to discuss about climate change, causes and impact and how we can cope with it.

Continue!

Rainwater Harvesting Systems in practice

What are the various types of rainwater harvesting systems? Let's find out more about them!

Continue!

Reduce-Reuse-Recycle

What is my water footprint and how can I reduce it?

Continue!

Water resources

Discovering the water resources of our region.

Continue!

Where do I begin?

Let's see why it is important to know about water in our region.

Continue!