Calculate L-CV and L-SKEW for a gauged catchment. Uses `lmoments3` library.

        Methodology source: Science Report SC050050, para. 6.7.5

def _l_cv_and_skew(self, catchment):
        """
        Calculate L-CV and L-SKEW for a gauged catchment. Uses `lmoments3` library.

        Methodology source: Science Report SC050050, para. 6.7.5
        """
        z = self._dimensionless_flows(catchment)
        l1, l2, t3 = lm.lmom_ratios(z, nmom=3)
        return l2 / l1, t3