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<p>Sea level change impact predictions on coastal environments are fraught with uncertainties especially in the absence of ecosystem-specific response patterns to a natural surrogate. Time-dependent variation in tidal forcing is an ideal surrogate to employ for comparative assessments. Results of simultaneous quarter-hourly monitoring of Calabar River and contiguous Anantigha groundwater levels within the mesotidal coast of S. E. Nigeria are presented for sequential low- and high-stand phases of 33 half-fortnightly tidal cycles. While their semi-diurnal tidal cycle water level curves show broad similarities, their curve shape characteristics convey statistically-contrasting dynamics. The river water level was rise rate-asymmetric (82%) at high-stand phase with no-asymmetry at low-stand phase. By contrast, groundwater consistently showed fall rate-asymmetry. The flood/ebb duration ratios showed the river as ebb-asymmetric (79%) at high-stand phase with no-asymmetry at low-stand counterpart. The groundwater consistently indicated &gt; 90% flood-duration asymmetry. The rise and fall rates of both water levels showed positive correlation with oscillation amplitude, the strongest being at low-stand phase for groundwater (r = 0.74 to 0.82). The relationship between the rise/fall rate ratio and flood/ebb duration ratio for both water bodies was characterized by strong inverse correlation (r = -0.95 to -0.99). Compared with the river, groundwater levels depicted about 2-fold lower %-deviation from its mean, 9-fold higher frequency of negative kurtosis (≥ -1.5) and more consistent symmetric (-0.3 to 0.3 range) distribution. The observed disparities suggest that sea level change impact prediction on coastal regions must be integrative of constituting ecosystems.</p>

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Coastal river and groundwater level response patterns to half-fortnightly low- and high-stand phase tidal forcing cycles: Implication for sea level change coastal impact predictions

  • 期刊论文

  • 发表日期：

    2025年8月5日

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  • Effiom E. Antia

摘要

Sea level change impact predictions on coastal environments are fraught with uncertainties especially in the absence of ecosystem-specific response patterns to a natural surrogate. Time-dependent variation in tidal forcing is an ideal surrogate to employ for comparative assessments. Results of simultaneous quarter-hourly monitoring of Calabar River and contiguous Anantigha groundwater levels within the mesotidal coast of S. E. Nigeria are presented for sequential low- and high-stand phases of 33 half-fortnightly tidal cycles. While their semi-diurnal tidal cycle water level curves show broad similarities, their curve shape characteristics convey statistically-contrasting dynamics. The river water level was rise rate-asymmetric (82%) at high-stand phase with no-asymmetry at low-stand phase. By contrast, groundwater consistently showed fall rate-asymmetry. The flood/ebb duration ratios showed the river as ebb-asymmetric (79%) at high-stand phase with no-asymmetry at low-stand counterpart. The groundwater consistently indicated > 90% flood-duration asymmetry. The rise and fall rates of both water levels showed positive correlation with oscillation amplitude, the strongest being at low-stand phase for groundwater (r = 0.74 to 0.82). The relationship between the rise/fall rate ratio and flood/ebb duration ratio for both water bodies was characterized by strong inverse correlation (r = -0.95 to -0.99). Compared with the river, groundwater levels depicted about 2-fold lower %-deviation from its mean, 9-fold higher frequency of negative kurtosis (≥ -1.5) and more consistent symmetric (-0.3 to 0.3 range) distribution. The observed disparities suggest that sea level change impact prediction on coastal regions must be integrative of constituting ecosystems.