# Useful helper functions

def travelTime(velocity, distance):
    '''Return time of travel for distance'''
    time = distance / velocity
    return time

def distanceTravelled(velocity, time):
    distance = velocity * time
    return distance

def velocity(distance, time):
    velocity = distance / time
    return velocity

def aveVertK(##):
    ######
    return ###

def aveHorizK(####):
    #####
    return ###

def retardation(###):
    #####
    return ###

def effectiveDiffusion(####):
    ######
    return De


# Useful helper functions

def travelTime(velocity, distance):
    '''Return time of travel for distance'''
    time = distance / velocity
    return time

def distanceTravelled(velocity, time):
    distance = velocity * time
    return distance

def velocity(distance, time):
    velocity = distance / time
    return velocity

def aveVertK(##):
    ######
    return ###

def aveHorizK(####):
    #####
    return ###

def retardation(###):
    #####
    return ###

def effectiveDiffusion(####):
    ######
    return De

def dilution(####):
    #######
    return ####

Add dilution placeholder