def pd1(shellmound_model):
    """Perioddata defined with start_date_time, nper, perlen, nstp, and tsmult
    specified explicitly.
    """
    m = shellmound_model
    m.cfg['sto']['steady'] = {0: True,
                              1: False}

    # Explicit stress period setup
    nper = 11  # total number of MODFLOW periods (including initial steady-state)
    m.cfg['tdis']['perioddata'] = {}
    m.cfg['tdis']['options']['start_date_time'] = '2008-10-01'
    m.cfg['tdis']['perioddata']['perlen'] = [1] * nper
    m.cfg['tdis']['perioddata']['nstp'] = [5] * nper
    m.cfg['tdis']['perioddata']['tsmult'] = 1.5
    m._perioddata = None
    pd1 = m.perioddata.copy()
    return pd1