Create NPS disaggregation factors for allocation assessment

Create NPS disaggregation factors for allocation assessment

Usage

util_aa_npsfactors(tbbase, rcclucsid, emc)

Arguments

tbbase

Data frame returned from util_nps_tbbase containing land use, soils, and jurisdiction data. Must include columns bay_seg, basin, drnfeat, entity, CLUCSID, hydgrp, and area_ha.

rcclucsid

Data frame of runoff coefficients by land use class and hydrologic soil group. See rcclucsid.

emc

Data frame of event mean concentrations by land use class. Must include columns clucsid and mean_tn. See emc.

Value

A named list with two elements:

rc

Data frame of RC factors: bay_seg, basin, entity, category, clucsid, factor_rc. factor_rc is each entity's fractional share of the weighted area × runoff coefficient within each basin × CLUCSID combination. Sums to 1 across all entities for each basin × CLUCSID.

tn

Data frame of TN factors: bay_seg, basin, clucsid, factor_tn. factor_tn is each CLUCSID's fractional share of basin TN load, weighted by area × event mean TN concentration. Sums to 1 across all CLUCSIDs for each basin.

Details

These factors are used internally by anlz_aa to disaggregate basin-level NPS loads to individual MS4 jurisdictions (entities).

Two factors are required because the disaggregation is a two-step process matching the original SAS workflow:

TN factor (factor_tn)

Distributes total basin TN load among land use classes. Based on area × event mean TN concentration per CLUCSID. Jurisdiction is not required, sums to basin total.

RC factor (factor_rc)

Distributes each land use class's TN and water loads among MS4 entities based on each entity's share of that land use type's weighted runoff (area × runoff coefficient). Jurisdiction is required here, i.e., tbbase includes the entity overlay.

Annual runoff coefficient: rc = (dry_rc * 8 + wet_rc * 4) / 12.

Basin remapping matches the SAS preprocessing: nested basins 02303000 and 02303330 are assigned to 02304500; 02301000 and 02301300 to 02301500; 02299950 to LMANATEE; basin 206-5 is assigned to bay_seg 55. Basin 02307359 is excluded entirely.

Non-contributing drainage features (drnfeat == "NONCON") and water/tidal CLUCSIDs (17, 21, 22) are excluded from both factors.

Compound hydrologic soil groups (e.g., "A/D") are simplified to their primary group ("A") before joining runoff coefficients.

These factors are specific to a land use layer and should be rebuilt whenever the underlying tbbase changes.

Examples

data(tbbase)
data(rcclucsid)
data(emc)
nps_factors <- util_aa_npsfactors(tbbase, rcclucsid, emc)