Short Introduction - theory
The basin model consists of multiple elements representing hydrologic features. These can be added by right-clicking on the Basin Model Map and selecting Add Element. The key elements include:
a) Subbasin
The subbasin is used to represent the physical watershed. Given precipitation, outflow from the subbasin element is calculated by subtracting precipitation losses, calculating surface runoff, and adding baseflow.
- Represents a watershed area where precipitation falls and is transformed into runoff.
- Define Name, Area, Loss Method (e.g., SCS Curve Number, Green-Ampt), and Transform Method (e.g., SCS Unit Hydrograph, Clark, Snyder, etc.).
🔹 Why? This is the core hydrologic unit where rainfall-runoff computations occur.
b) Reach
The reach is used to convey streamflow in the basin model. Inflow to the reach can come from one or many upstream elements. Outflow from the reach is calculated by accounting for translation and attenuation. Channel losses can optionally be included in the routing.
- Represents a river or stream where water flows downstream.
- Define Routing Method (e.g., Muskingum, Lag, Kinematic Wave).
🔹 Why? This element helps model the movement of water through the river network.
c) Junction
- Represents a confluence point where multiple flows meet.
- No additional methods need to be set; it simply sums the inflows.
🔹 Why? It ensures proper water balance in the watershed model.
d) Reservoir
- Represents a lake or dam where water storage and controlled release occur.
- Define Storage-Discharge Method (e.g., Elevation-Storage-Discharge, Outflow Curve, or Level Pool Routing).
🔹 Why? Important for flood control and water management studies.
e) Diversion
- Represents water being diverted from the main channel.
- Define Diversion Method (e.g., Constant Flow, Rating Curve).
🔹 Why? Useful for irrigation and water supply modeling.
f) Source/Sink
- Source: Represents additional inflows, such as groundwater contributions.
- Sink: Represents the final outlet where water leaves the system.
🔹 Why? Essential for representing external inflows or points where water exits the system.
How to compose a basin with its hydrologic elements step by step
Hydrologic elements can be added to the basin map after it is created. Select the basin model in the Watershed Explorer to open the basin map. If background map layers are available, add them to the basin model before adding elements.
Add an element by selecting one of the tools from the toolbar, and clicking the left mouse button on the desired location in the basin map. Connect an element to a downstream element by right-clicking the upstream element to access the Connect Downstream menu item.
1) Add the sub-basins. They will just appear isolated in the space. In this example the sub-basins are: Comasinella, Paderno Dugnano, Lentate.
2) Add the junctions. They also appear as isolated objects in the space. In this example the junctions are: Cinisello, Malnate.
3) Add the reach. It appears as a blue line. You have to give it a name when you create it, but its name doesn't show up in the map.
4) Connect the elements. In order to connect the upstream element to the downstream one:
Select the blak arrow button (the first button in the list). This button gives you the possibility to select every hydrological element in the map.
Select an element and then right-click on it. A window will show up. Select Connect Downstream, and then click on the element that you want to be the downstream one. In the example I connected Comasinella (upstream) with Cinisello (downstream).
As shown below, a thin black line appears, connecting the two elements.
After connecting all the elements, we will have the following result:
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