config/parameters.py — unused entries, duplicate literal values, and dual-purpose parameter

[danbroman]

Cleanup notes for config/parameters.py

While reviewing config/parameters.py against the rest of the codebase, I found a few issues worth tracking for later cleanup.

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1. A couple of hardcoded values in reservoirs/state.py that should really be named parameters

There are two bare numbers in reservoirs/state.py that aren't defined anywhere in parameters.py.

Line 24:

self.reservoir_storage_operation_year_start = 0.85 * grid.reservoir_storage_capacity

This sets the initial fill level (as a fraction of capacity) for reservoir_storage_operation_year_start — basically a snapshot of storage taken at the start of each operating year, used later in the Biemans k-factor calculation.

Line 27:

default_storage = 0.9 * grid.reservoir_storage_capacity

This is just the default starting reservoir storage used when no initial storage is provided.

Suggested fix: add two new parameters and pass them into initialize_reservoir_state():

reservoir_initial_op_year_storage_fraction = 0.85   # cold-start fill for op-year-start storage
reservoir_default_initial_storage_fraction = 0.9    # default value when no value is provided in the reservoir parameters file

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2. A few parameters that aren't actually used anywhere

Three entries in Parameters.__init__ are defined but never referenced anywhere else in the code:

Parameter	Value	Comment in file
small_value	1.0e-10	"small value, for less precise arithmetic"
effective_tracer_velocity	10.0	"liquid/ice effective velocity" (already flagged with a TODO)
ICE_TRACER	1	Paired with LIQUID_TRACER, but the ice path was never built

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3. One parameter is doing two unrelated jobs

reservoir_runoff_capacity_parameter = 0.1 is currently used for two unrelated purposes:

1. Minimum storage floor (reservoirs/grid.py:65,69) — used as a fallback for reservoir_minimum_storage when CAP_MIN is missing or invalid. Here it's interpreted as a fraction of storage capacity.
2. Runoff-capacity threshold (reservoirs/release.py:67, reservoirs/regulation.py:46) — used as a threshold in the Biemans release condition and as a minimum-flow floor during regulation. Here it's interpreted as a flow-to-capacity ratio.

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4. General state of parameters.py

There's already a TODO on line 10 acknowledging that documentation and configurability need work. A lot of entries are missing docstrings or units, which makes it harder to tell what's safe to change. As a follow-up, it'd be good to add units and short descriptions to each parameter, and think about whether some of these should live in config_defaults.yaml instead of being hardcoded, edit-only Python constants.