Hydrographs lab preparation
Hydrographs lab preparation
Embedded Files
Associated lecture materials
Associated lecture materials
To prepare for lab activities, first be sure you have reviewed the associated materials from lectures on hydrograph interpretation.
Contents of this module
Contents of this module
Integrating total volumes
Integrating total volumes
The most robust methods for calculating temporal summary statistics of stream flow starts with knowing how to calculate the total volume of flow over a given period of time. This calculation is an exercise in numerical integration. Here is a detailed description of editing a spreadsheet to integrate the total volume of flow over a day from an instantaneous flow hydrograph. The steps of numerical integration should look familiar relative to the dilution gauging lab activities. The dimensions being integrated are different, but the numerical approaches are identical (8:57 min).
Downloading and importing data
Downloading and importing data
The USGS provides several tools that are helpful for downloading data from their database. The first is a data visualization tool that allows you to review the data before downloading. This tool was introduced briefly in lecture (6:17 min).
To start exploring your own spreadsheet calculations on hydrographs from watersheds of your choice in the USGS database, you first need to know how to download data in a form that can be imported to Excel. We are going to use the query building tool for the Application Programming Interface (API) to the USGS database. The result will be a URL configured to request daily mean flow data via the Internet, which can then be used by most data analysis tools (including Excel's power query tool) to pull the data directly into the analytical workflow (12:45 min).
Once you have a URL for a query to the USGS database API, you will need to use the Excel power query tool to import the data and prepare it for analysis (20:10 min).
NOTE FOR MAC USERS: After making the video below, we discovered that the power query tool in the Mac version of Excel apparently does not allow for the direct download of data from a URL query to the web. To work around this problem, you can put the URL query in a web browser to directly download the data as a csv text file, as demonstrated at time 12:00 in the previous video. Then you can go through the steps in the following video, but import the data as the downloaded csv text file rather than a web URL. All the steps should be the same except for choosing where to get the csv text data.
Flow duration and flood frequency analyses
Flow duration and flood frequency analyses
Once you have watershed data, you are ready to start playing with the typical approaches to watershed analysis for any hydrograph you choose! For this lab activity, you are asked to perform annual flow duration curve analyses, comparing and contrasting watersheds with different "flashiness" and storage capacity. Here is a detailed description of building an Excel spreadsheet to calculate the exceedance probabilities necessary for a flow duration curve analysis (14:47 min).
Remaining lab activities will ask you to do a risk analysis based on a flood frequency curve. The following two lecture videos are especially relevant to this lab. No need to study these again if you are comfortable with the concepts after study of the lecture materials. You should be particularly sure you understand the lecture materials regarding reading flood frequency curve graphs... (7:13 min)
and compounding exceedance probabilities over multiple years (9:57 min).
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