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Nonpoint Source Water Pollution

Nonpoint Source > Watershed Assessment > Water Monitoring and You > Interpreting Data Interpreting Data

Interpreting and analyzing data is a crucial step in the development of any watershed plan. The data analysis supports the identification of watershed pollutant sources and causes of impairment, which is essential to defining watershed management needs. Through careful analysis you’ll obtain a better understanding of major pollutant sources, the behavior of these sources, and their impacts on waterbodies. An understanding of the watershed conditions and sources is also the basis for determining the appropriate method for quantifying pollutant loads.

The process of conducting data analyses to characterize your watershed and its pollutant sources begins with broad assessments such as evaluating the averages, minimums, and maximums of measured parameters at all watershed stations. Data analysis helps to evaluate spatial, temporal, and other identifiable trends and relationships in water quality. Instream data analysis is needed to identify the location, timing, or behavior of potential watershed sources and their effect on watershed functions such as hydrology, water quality, and aquatic habitat. Habitat data analysis is needed to identify areas that need to be restored or protected.

One way to organize and focus the data analysis is to consider the specific watershed characteristics and the questions that need to be answered before an appropriate management strategy can be developed. U.S. EPA’s Handbook for Developing Watershed Plans to Restore and Protect Our Waters is an excellent resource to educate yourself and your stakeholders on this topic. In particular, U.S. EPA’s worksheet 7-1 can help to determine the types of analyses you might need to conduct for water quality. U.S. EPA’s worksheet 7-2 can help to determine the types of analyses you might need to conduct for habitat assessment and protection.

Remember that data gathering and analysis is an ongoing, iterative process. Data examined in this phase will continue to be used in subsequent activities, such as identifying and evaluating management measures and tracking implementation efforts.

Additional Resources

  • Section 319 Guidance Document on Water Quality Targets:
    • This document includes a summary of water quality parameters that watershed groups are often concerned with, the associated Indiana Water Quality Standard (where applicable), and example targets and references for parameters for which standards currently do not exist.
  • Data2Maps (D2M):
    • Locally-led watershed projects need to be able to demonstrate the water quality data of their local area in order to attract support. Being able to show people where the problems are in the watershed is an important tool for building public support. D2M is a custom Excel application in which users can overlay their sampling data on static maps and do preliminary assessment and analyses. The outputs can be printed directly from D2M or pasted into other applications (e.g., PowerPoint, MSWord) for outreach and reporting materials.
  • Integrated Report - External Data:
    • The external data framework was developed by the Indiana Department of Environmental Management Office of Water Quality (OWQ) to provide a systematic, transparent, and voluntary process for external organizations to submit their water quality data for consideration in various OWQ programs. The external data framework describes OWQ policy regarding the agency use of external data, the guidelines for submitting data and the technical assistance necessary to facilitate greater collaboration between OWQ and external parties.