Watershed annual water balance
Introduction
The objective of this unit is to introduce students to the concept of watershed annual water balance, and have them apply it to a watershed to estimate the total annual evapotranspiration depth. The steps involved in the unit require students to determine the annual precipitation depth and the effective depth of total annual streamflow for the given watershed, and then apply the water balance equation with reasonable assumptions.
Intended Audience
This unit is intended for university students of all levels in hydrology, environmental engineering/sciences and geology/earth sciences
Conceptual Learning Outcomes
- Students demonstrate the understanding of law of mass conservation in watershed hydrology along with the concepts of control volume and flux.
- Students demonstrate the understanding of different components of a watershed balance.
- Students develop the understanding of relative magnitudes of different fluxes of water leaving and entering the watershed.Practical Learning Outcomes
- Students demonstrate the use of online data sources or web services for obtaining historical streamflow and precipitation data.
- Students learn to calculate the total annual depths of precipitation and streamflow from time series records using MS Excel.
- Students learn to account for different fluxes as they develop the watershed balance equation for their study areas.
Student Time Required
2.5 hours
Supporting Reference Documents and Files
Streamflow time series (Excel 2007 (.xlsx) 1.5MB Sep7 15)
Precipitation time series (Excel 2007 (.xlsx) 26kB Sep7 15)
Instructions
To start with, you need to download the instantaneous streamflow data [Step 1] and 15-min precipitation data [Step 2] for your chosen area of study and time period. Next, convert the downloaded text files into simple time series in excel. Here, as starter data, we have enclosed the streamflow and precipitation time series (15-minute) excel files for Hall Creek in Indiana for the year 2000. Next step [Step 3] requires you to calculate the total annual depth of streamflow from the streamflow time series. Similarly, you can calculate the total annual precipitation [Step 4] for your study area. Above steps give you two major fluxes of water entering or leaving the system in the given time frame. Final step [Step 5] requires you to apply the concept of mass conservation to your watershed, making reasonable assumptions about certain unknown fluxes, to estimate the total annual evapotranspiration depth.