def philly_storm_intensity(tc, return_period=0):
    """
	given a tc, return the intensity of the
	Philadelphia Water Dept design storm (in/hr)
	"""
    I = 116.0 / (tc + 17.0)
    if return_period == 1:
        I = 100.0 / (tc + 18.0)
    if return_period == 2:
        I = 131.0 / (tc + 21.0)
    if return_period == 5:
        I = 171.0 / (tc + 23.5)
    if return_period == 10:
        I = 214.0 / (tc + 26.0)
    if return_period == 25:
        I = 252.0 / (tc + 28.0)
    if return_period == 50:
        I = 289.0 / (tc + 30.0)
    if return_period == 100:
        I = 325.0 / (tc + 32.0)
    return I
