def simulate_water_quality(tree, cell_res, fn,
parent_cell=None, current_cell=None):
"""
Perform a water quality simulation by doing simulations on each
type of cells (leaves), then adding them together going upward
(summing the values of a node's subtrees and storing them at that
node).
`parent_cell` is the cell type (a string with a soil type and land
use separated by a colon) of the parent of the present node in
tree.
`current_cell` is the cell type for the present node.
`cell_res` is the size of each cell (used for turning inches of
water into volumes of water).
`tree` is the (sub)tree of cell distributions that is currently
under consideration.
`fn` is a function that takes a cell type and a number of cells
and returns a dictionary containing runoff, et, and inf as
volumes. This typically just calls `simulate_cell_year`, but can
be set to something else if e.g. a simulation over a different
time-scale is desired.
"""
# Internal node.
if 'cell_count' in tree and 'distribution' in tree:
# simulate subtrees
tally = {}
for cell, subtree in tree['distribution'].items():
simulate_water_quality(subtree, cell_res, fn, current_cell, cell)
subtree_ex_dist = subtree.copy()
subtree_ex_dist.pop('distribution', None)
tally = dict_plus(tally, subtree_ex_dist)
# update this node
tree.update(tally)
# Leaf node.
elif 'cell_count' in tree and 'distribution' not in tree:
# runoff, et, inf
n = tree['cell_count']
result = fn(current_cell, n)
tree.update(result)
# water quality
if n != 0:
runoff = result['runoff-vol'] / n
liters = get_volume_of_runoff(runoff, n, cell_res)
land_use = current_cell.split(':')[1]
if is_bmp(land_use) or land_use == 'no_till' or \
land_use == 'cluster_housing':
land_use = parent_cell.split(':')[1]
for pol in get_pollutants():
tree[pol] = get_pollutant_load(land_use, pol, liters)
def simulate_cell_day(precip, evaptrans, cell, cell_count):
"""
Simulate a bunch of cells of the same type during a one-day event.
`precip` is the amount of precipitation in inches.
`evaptrans` is evapotranspiration.
`cell` is a string which contains a soil type and land use
separated by a colon.
`cell_count` is the number of cells to simulate.
The return value is a dictionary of runoff, evapotranspiration, and
infiltration as volumes of water.
"""
def clamp(runoff, et, inf, precip):
"""
This function ensures that runoff + et + inf <= precip.
NOTE: Infiltration is normally independent of the
precipitation level, but this function introduces a slight
dependency (that is, at very low levels of precipitation, this
function can cause infiltration to be smaller than it
ordinarily would be.
"""
total = runoff + et + inf
if (total > precip):
scale = precip / total
runoff *= scale
et *= scale
inf *= scale
return (runoff, et, inf)
precip = max(0.0, precip)
soil_type, land_use, bmp = cell.lower().split(':')
# If there is no precipitation, then there is no runoff or
# infiltration; however, there is evapotranspiration. (It is
# understood that over a period of time, this can lead to the sum
# of the three values exceeding the total precipitation.)
if precip == 0.0:
return {
'runoff-vol': 0.0,
'et-vol': 0.0,
'inf-vol': 0.0,
}
# If the BMP is cluster_housing or no_till, then make it the
# land-use. This is done because those two types of BMPs behave
# more like land-uses than they do BMPs.
if bmp and not is_bmp(bmp):
land_use = bmp or land_use
# When the land-use is a built-type and the level of precipitation
# is two inches or less, use the Pitt Small Storm Hydrology Model.
# When the land-use is a built-type but the level of precipitation
# is higher, the runoff is the larger of that predicted by the
# Pitt model and NRCS model. Otherwise, return the NRCS amount.
if is_built_type(land_use) and precip <= 2.0:
runoff = runoff_pitt(precip, land_use)
elif is_built_type(land_use):
pitt_runoff = runoff_pitt(2.0, land_use)
nrcs_runoff = runoff_nrcs(precip, evaptrans, soil_type, land_use)
runoff = max(pitt_runoff, nrcs_runoff)
else:
runoff = runoff_nrcs(precip, evaptrans, soil_type, land_use)
inf = max(0.0, precip - (evaptrans + runoff))
(runoff, evaptrans, inf) = clamp(runoff, evaptrans, inf, precip)
return {
'runoff-vol': cell_count * runoff,
'et-vol': cell_count * evaptrans,
'inf-vol': cell_count * inf,
}
def simulate_cell_day(precip, evaptrans, cell, cell_count):
"""
Simulate a bunch of cells of the same type during a one-day event.
`precip` is the amount of precipitation in inches.
`evaptrans` is evapotranspiration.
`cell` is a string which contains a soil type and land use
separated by a colon.
`cell_count` is the number of cells to simulate.
The return value is a dictionary of runoff, evapotranspiration, and
infiltration as volumes of water.
"""
soil_type, land_use, bmp = cell.lower().split(':')
# If there is no precipitation, then there is no runoff or
# infiltration. There is evapotranspiration, however (is
# understood that over a period of time, this can lead to the sum
# of the three values exceeding the total precipitation).
if precip == 0.0:
return {
'runoff-vol': 0.0,
'et-vol': cell_count * evaptrans,
'inf-vol': 0.0
}
# Deal with the Best Management Practices (BMPs). For most BMPs,
# the infiltration is read from the table and the runoff is what
# is left over after infiltration and evapotranspiration. Rain
# gardens are treated differently.
if bmp and is_bmp(bmp) and bmp != 'rain_garden':
inf = lookup_bmp_infiltration(soil_type, bmp) # infiltration
runoff = precip - (evaptrans + inf) # runoff
return {
'runoff-vol': cell_count * runoff,
'et-vol': cell_count * evaptrans,
'inf-vol': cell_count * inf
}
elif bmp and bmp == 'rain_garden':
# Here, return a mixture of 20% ideal rain garden and 80% high
# intensity residential.
inf = lookup_bmp_infiltration(soil_type, bmp)
runoff = precip - (evaptrans + inf)
hi_res_cell = soil_type + ':hi_residential:'
hi_res = simulate_cell_day(precip, evaptrans, hi_res_cell, 1)
hir_run = hi_res['runoff-vol']
hir_et = hi_res['et-vol']
hir_inf = hi_res['inf-vol']
return {
'runoff-vol': cell_count * (0.2 * runoff + 0.8 * hir_run),
'et-vol': cell_count * (0.2 * evaptrans + 0.8 * hir_et),
'inf-vol': cell_count * (0.2 * inf + 0.8 * hir_inf)
}
# At this point, if the `bmp` string has non-zero length, it is
# equal to either 'no_till' or 'cluster_housing'.
land_use = bmp or land_use
# When the land use is a built-type and the level of precipitation
# is two inches or less, use the Pitt Small Storm Hydrology Model.
# When the land use is a built-type but the level of precipitation
# is higher, the runoff is the larger of that predicted by the
# Pitt model and NRCS model. Otherwise, return the NRCS amount.
if is_built_type(land_use) and precip <= 2.0:
runoff = runoff_pitt(precip, land_use)
elif is_built_type(land_use):
pitt_runoff = runoff_pitt(2.0, land_use)
nrcs_runoff = runoff_nrcs(precip, evaptrans, soil_type, land_use)
runoff = max(pitt_runoff, nrcs_runoff)
else:
runoff = runoff_nrcs(precip, evaptrans, soil_type, land_use)
inf = precip - (evaptrans + runoff)
return {
'runoff-vol': cell_count * runoff,
'et-vol': cell_count * evaptrans,
'inf-vol': cell_count * max(inf, 0.0),
}