set FractionalFlow inflow equal to outflow (#736)

Fixes #733

core/src/solve.jl

@@ -989,7 +989,10 @@ function formulate_flow!(
     for (i, id) in enumerate(node_id)
         downstream_id = only(outneighbors(graph_flow, id))
         upstream_id = only(inneighbors(graph_flow, id))
-        flow[id, downstream_id] = flow[upstream_id, id] * fraction[i]
+        # overwrite the inflow such that flow is conserved over the FractionalFlow
+        outflow = flow[upstream_id, id] * fraction[i]
+        flow[upstream_id, id] = outflow
+        flow[id, downstream_id] = outflow
     end
     return nothing
 end

core/test/run_models.jl

@@ -55,6 +55,15 @@ end
     )
     # flows are recorded at the end of each period, and are undefined at the start
     @test unique(table.time) == Ribasim.datetimes(model)[2:end]
+
+    # inflow = outflow over FractionalFlow
+    t = table.time[1]
+    @test length(p.fractional_flow.node_id) == 3
+    for id in p.fractional_flow.node_id
+        inflow = only(table.flow[table.to_node_id .== id .&& table.time .== t])
+        outflow = only(table.flow[table.from_node_id .== id .&& table.time .== t])
+        @test inflow == outflow
+    end
 end
 
 @testset "basic transient model" begin

docs/core/usage.qmd

@@ -506,7 +506,7 @@ node_id       | Int     | -            | sorted
 active        | Bool    | -            | (optional, default true)
 length        | Float64 | $m$          | positive
 manning_n     | Float64 | $s m^{-\frac{1}{3}}$          | positive
-profile_with  | Float64 | $m$          | positive
+profile_width | Float64 | $m$          | positive
 profile_slope | Float64 | -            | -
 control_state | String  | -            | (optional)