Statistical datum corrections to measured water levels for achieving inter-gage consistency in a large seasonally ponded wetland

Abstract

Accurate, consistent water surface elevations (stages) among gages within a large waterbody are essential for accurate hydrological analyses. This study developed and tested a process of statistical stage bias-correction and quantified corrections needed to maintain consistency among gages. Ponded conditions with consistent water-surface elevations were identified within an Everglades wetland area using four screening criteria: three-day antecedent rainfall ≤ 0.25 mm/day, seven-day antecedent rainfall ≤ 5.1 mm/week, mean stage change from prior day ≤ 0.15 m, and difference between median marsh and canal stages ≤ 0.015 m. Historical stage values were adjusted based on long-term mean inter-gage bias. Adjustments up to 0.0472 m were needed to offset mean inter-gage bias among 12 canal and five marsh gages. Bias-corrected stages improved consistency over an independent one-year period. These methods apply to deriving statistical bias-correction values in other seasonally ponded water bodies and identifying gages requiring datum maintenance.