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Stream Measures (Vandløbstiltag)

Stream-level P reduction measures applied to individual watercourses (w). Decision variable: v_w(w, w_m) ∈ {0,1}. P effects aggregate at up_lakecatch level.

Constraint: v_w(w,"re_meandering") + v_w(w,"raising") ≤ 1 — these two restoration types cannot be combined on the same watercourse.

Ochre traps (Okkeranlæg)

Parameter Value
Target P (via ochre/iron-bound P in drainage water)
P effect P_Effects_Ochre(w) = 140 kg P/yr [classes 1 and 2 only]
Cost Cost_W(w,"Ochre") = 121,537 DKK (fixed, per trap)
Potential w_okker(w) — binary indicator of ochre drainage potential
Equation Ochre_P_eff(up_lakecatch) = Σ w_okker(w) × 140 × v_w(w,"ochre")

Notes: Ochre (iron oxyhydroxide) precipitates P in alkaline conditions. High effect per trap but high installation cost. Only classes 1 and 2.

Sand traps (Sandfang)

Parameter Value
Target P (via P attached to eroded sand particles)
P effect 7–26 kg P/yr depending on watercourse class and geographic zone
Cost 9,328 DKK (class 1) or 12,460 DKK (class 2)
Potential w_sand(w) — binary
Geographic zones Zone 2: 26 kg P/yr; Zone 3: 12 kg P/yr; Zone 1: 7 kg P/yr
Equation Sand_P_eff(up_lakecatch) = Σ w_sand(w) × P_Effects_Sand(w) × v_w(w,"sand")

Notes: Class 3 sandtraps were considered but excluded (costs were estimated as uncertain — noted in code as "made up"). Only classes 1 and 2 retained.

Re-meandering (Genslyngning)

Parameter Value
Target P (via increased retention, sedimentation, and reduced bank erosion)
P effect w_P_red_re_meandering(w) — watercourse-specific (from w_P_red_re_meandering.inc)
Cost Class 1: 7,000 DKK/km + re_meandering_xcost(w); Class 2/3: 25,000 DKK/km + xcost
Potential w_meandering(w) — binary potential indicator
Mutual exclusion Cannot combine with raising on same watercourse

Notes: Re-meandering restores straightened streams to their natural meandering course. The extra costs (re_meandering_xcost) are calculated outside the model (e.g. for acquiring riverside land). Class 2 and 3 cost the same.

Raising (stream bed raising / Hævning)

Parameter Value
Target P (via reduced flow velocity and increased sedimentation)
P effect w_P_red_raising(w) — watercourse-specific (from w_P_red_raising.inc)
Cost Class 1: 5,000 DKK/km; Class 2: 8,000 DKK/km; Class 3: 19,000 DKK/km
Potential w_raising(w) — binary potential indicator
Mutual exclusion Cannot combine with re-meandering

Notes: Raising the streambed reduces drainage velocity and encourages P sedimentation in the stream. This conflicts with re-meandering which also restores natural flow dynamics.

Trees on erosion stretches (Træplantning ved erosionsstrækninger)

Technically a stream-adjacent measure, indexed by erosion stretch (ero_stretch), not watercourse.

Parameter Value
Target P (via bank stabilization and reduced erosion)
P effect tree_eff(ero_stretch) kg P/yr — stretch-specific
Cost Cost_S(ero_stretch, "trees") = 290.8 DKK/yr per stretch (very low)
Decision variable v_str(ero_stretch, "trees")
See also Trees page

Data sources

  • Watercourse class: w_class.inc
  • Lengths: w_length_km.inc
  • Potentials: w_ochre.inc, w_sand.inc, w_meandering.inc, w_raising.inc
  • Geographic zones: Set_geo.inc, Set_WGeo.inc
  • P effects: w_P_red_re_meandering.inc, w_P_red_raising.inc
  • Extra costs: re_meandering_xcost.inc
  • Spatial linkage: set_kw.inc, set_up_lakew.inc