Generally, the average harvested power and accumulated charge per hour significantly changed when scouring occurred, as can be observed from their pseudo-spectra in Figure 5. Let us take a close look in the narrow frequency band under 10 Hz (Figure 5(b)). When the water flowed with a frequency around 6 Hz, the MEH could harvest the most energy from the non-scouring pier but its harvested energy dramatically dropped when scouring occurred. The drop of the harvested energy could be attributed to the scouring induced change in the pier’s modal properties. It is known from the modal analysis that the first inplane bending mode had a modal frequency of 5.89 Hz, which was easily excited by the water flow force of a close resonant frequency acting in the same plane. When scouring occurred, this mode dropped its modal frequency to 4.76 Hz and was therefore less easily excited by the water flow force of the aforementioned frequency. Contrarily, when the water flowed with a frequency around 5 Hz, the MEH could harvest not much energy from the non-scouring pier but could harvest more when scouring occurred, being attributed to the close resonance of the water flow frequency to the first in-plane bending modal frequency of the scouring pier. As for the frequency peaked around 45 Hz in the pseudospectra (Figure 5(a)), it is likely to be the MEH’s natural frequency, which was essentially not affected by the scouring and was of our little interest. It is indicated in this numerical simulation that the energy harvested from the pier cap was sensitive to the scouring of the specific pattern considered herein, implying that the harvested energy could be a potential scouring indicator if the water flow constantly covered the frequency band that was closely resonant to the pier’s modal frequency.