Hydrological analysis using GIS requires that several aspects of the water cycle – occurrence, movement, and their relationship with the environment – be understood and addressed. Hydrology includes the study of surface and groundwater. Surface water has been understood well over the years and tools and models are available. However, groundwater has not been so well understood as for this, hydrogeological aspects also need to be incorporated.
ArcGIS from ESRI provides the tools for hydro analysis. ArcHydro is a set of data models and tools that allow you to study surface and groundwater. Surface water can be studied using ArcGIS Hydrology Toolset or ArcHydro. For Groundwater, use ArcHydro Groundwater (that has been developed by AQUAVEO and ESRI) or ArcGIS groundwater toolset (that is part of ArcGIS). Use ArcHydro Groundwater to:
- Create maps depicting water levels, water quality, etc
- Create and visualize both 2D and 3D geologic models and subsurface analysis
Use ArcGIS Groundwater Toolset for Spatial Analysis (Darcy analysis, particle tracking, etc).
Here we will look at how to use Arc Hydro Groundwater to study wells around an aquifer and understand the water level
changes over time by generating time series plots of water level data for selected wells. For this the overall steps would include the following:
- Importing a map of the area including aquifers
- Importing well data
- Mapping the feature type in ArcGIS Hydro to column names in the data imported
- Filtering the well data to specific types of wells
- Symbolizing the filtered wells
- Assigning Hydro IDs
- Importing time series data for water level measurements of a particular well at a particular time
- Create relationship between column in data file and feature type in ArcGIS
- Join the time series data to well data based on a field
- Calculate the elevation as well depths are negative values
- Find wells with transient data using Make Time Series statistics
- Create graphs and Interpolate data to a raster to create map of water levels for specific period
- Generate flow direction for the wells
The procedure with a few screen shots is discussed here. For an elaborate discussion and detailed procedures refer to the ESRI and AQUAVEO websites.
Importing a map of the area with aquifers
The tool bars for groundwater analysis
Importing well data
Mapping the feature type in ArcGIS Hydro to column names in the data imported
The field data collected must be in text files, spreadsheets, or supported formats. Although, various data can be collected the Arc Hydro data model will have a few features to which the collected data must be mapped. This data is specified by the Arc Hydro Framework and research is underway to improve the models.
Note that these wells have a state well number, associated aquifer code, and names of owners that helps in managing groundwater.
Filtering the well data to specific types of wells
Wells can be classified on different parameters and labeled accordingly. For example, wells can be for monitoring, agricultural, or drinking water purposes or can be classified according to the geology – sandstone aquifer wells, igneous wells, etc.
Assigning Hydro IDs
Hydro features are identifiers of hydrological and hydrogeological components. Hydro ID is unique across the geodatabase that is needed to build a model of the well or aquifer. Hydro Code is also unique and describes the features in an external data source. This is a key step.
Importing time series data for water level measurements of a particular well at a particular time and Creating relationship between column in data file and feature type in ArcGIS
Join the time series data to well data based on a field
We have already imported well data and symbolized it. Next for analysis, a second parameter is required. For this we imported time-based data as the purpose is to study water levels over time. Next we join the time series data collected at the particular well to the well data. This is where the Hydro ID is useful as it is unique.
Calculate the elevation as well depths are negative values
Remember that wells are beneath the surface and is assigned negative values. However, this needs to be “normalized” for calculation and for meaningful inference of the data. This is done using the elevation and time series values.
Find wells with transient data using Make Time Series statistics
Now that you have well data and time series data and assigned unique Hydro IDs, you can do further analysis. One of the important tasks is to separate out the wells without time-bound data. This happens as some wells might have gone dry or simply data might not have been captured or the wells might not be significant for the study.
You can use the Make Time Series statistics tool to find features such as wells with transient data for specific periods.
Creating graphs: Graphical representations help you study the selected wells and make decisions. You can use the Time Series Grapher to do this.
Interpolating data to raster catalog: you can create raster maps such as water level maps for future use using the Spatial Analyst tools.
Generate flow direction for the wells: you can find out the direction of water flow using the flow direction generator tool. This helps in identifying the downward gradient and where water flows into.
This concludes the overview of the steps to study water levels in wells around an aquifer.