A method for hydrometric data rescue: Challenges and solutions for working with archival data

The availability of long, quality-controlled discharge records is crucial for hydrological research that supports water resource planning, extreme flow estimation and investigations into the effects of climate variability and anthropogenic disturbances on river flow regimes. Archival hydrometric data sources (e.g. historical staff gauge readings, autographic chart data, and historical flow measurements) provide an invaluable opportunity to extend available discharge records, however a process of transcription and digitisation known as data rescue is required to make them available to the public.

In their 2014 ‘Guidelines for Hydrological Data Rescue’, the World Meteorological Organisation (WMO) provided generalised guidance to encourage Members to engage in data rescue activities to mitigate the very real risk of data loss due to physical record deterioration. Yet few published examples exist. Our work to extend discharge records for eight river stations across Ireland provides a detailed applied example that expands the methodology outlined in the WMO guidance by addressing two core challenges encountered: i) how to collect reliable data in the face of quality issues specific to historical autographic chart data; and ii) how to effectively communicate the level of confidence in the rescued data to the end user. We present procedures for data processing, quality assurance using quality codes, and compilation of key metadata and information about each measurement station. Lessons learnt are summarised in a generalised workflow and presented to the hydrology community to assist other hydrometric data rescue efforts.