diff --git a/.gitignore b/.gitignore
index bef9e39f..e97805ab 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,6 +44,7 @@ __old__
 mage8/
 adists/
 rubarbe/
+rubar/
 
 linux/
 windows/
diff --git a/src/Solver/RubarBE.py b/src/Solver/RubarBE.py
index ea5f21a1..11f571cc 100644
--- a/src/Solver/RubarBE.py
+++ b/src/Solver/RubarBE.py
@@ -194,7 +194,8 @@ class Rubar3(CommandLineSolver):
         self._export_stricklers(hydraulics, repertory, qlog, name=name)
         self._export_boundaries(hydraulics, repertory, qlog, name=name)
         if solid is not None:
-            self._export_hydros(solid, repertory, qlog, name=name)
+            self._export_hydros(solid, hydraulics["tinit"], repertory, qlog,
+                                name=name)
         if trased:
             self._export_condins(geometry, hydraulics["tinit"], repertory,
                                  qlog, name=name)
@@ -432,13 +433,14 @@ class Rubar3(CommandLineSolver):
         }
 
     @staticmethod
-    def _ignore_empty(bcs, node, warnings):
+    def _ignore_empty(bcs, node, warnings, meaningful=()):
         """A boundary condition without value carries no data: it is
-        ignored with a warning. Return (kept, ignored)"""
+        ignored with a warning, except for the types where an empty
+        condition has a meaning. Return (kept, ignored)"""
         trad = RunSolverTranslate()
         kept, ignored = [], []
         for bc in bcs:
-            if len(bc) == 0:
+            if len(bc) == 0 and bc.bctype not in meaningful:
                 warnings.append(trad["boundary_empty_ignored"].format(
                     name=bc.name, node=node.name))
                 ignored.append(bc)
@@ -447,10 +449,10 @@ class Rubar3(CommandLineSolver):
         return kept, ignored
 
     def _select_boundaries(self, bcs, expected, node, required_by, setting,
-                           warnings):
+                           warnings, meaningful=()):
         trad = RunSolverTranslate()
         selected = {}
-        bcs, ignored = self._ignore_empty(bcs, node, warnings)
+        bcs, ignored = self._ignore_empty(bcs, node, warnings, meaningful)
 
         for bc in bcs:
             kind = self._boundary_kinds[bc.bctype]
@@ -487,7 +489,9 @@ class Rubar3(CommandLineSolver):
         at the upstream node when TRASED is enabled and CONDAM=1 (CONDAM=2
         is refused), and has no downstream solid condition (rubar_init.f90,
         inits). Without sediment transport the solid conditions are
-        ignored. Return the condition or None"""
+        ignored. At the upstream node, an empty solid condition means a
+        supply at equilibrium in Pamhyr2 (Mage 'default'), written as a
+        negative Qs (_export_hydros). Return the condition or None"""
         if not trased:
             return None
         trad = RunSolverTranslate()
@@ -509,7 +513,7 @@ class Rubar3(CommandLineSolver):
         selected = self._select_boundaries(
             [bc for bc in solid if bc.node == edge.node1], expected,
             edge.node1, {"SL": f"TRASED=O, CONDAM={condam}"},
-            f"CONDAM={condam}", warnings
+            f"CONDAM={condam}", warnings, meaningful=("SL",)
         )
         bc = selected.get("SL")
         if bc is None:
@@ -1083,16 +1087,21 @@ class Rubar3(CommandLineSolver):
             lines = [header(len(bc))] + records(bc, columns)
             self._write_parameters(repertory, f"{filename}.{name}", lines)
 
-    def _export_hydros(self, bc, repertory, qlog, name="0"):
+    def _export_hydros(self, bc, tinit, repertory, qlog, name="0"):
         """HYDROS: number of points, then Qs, t, D, S (notice annex 1).
         Qs is a solid discharge (kg/s) or a concentration (kg/m3)
-        according to UNISOL, D and S are those of the condition"""
+        according to UNISOL, D and S are those of the condition. An
+        empty condition (supply at equilibrium) is written as a single
+        negative Qs: RubarBE then takes the transport capacity of the
+        upstream section at each time step (notice §3.6; rubarbe.f90,
+        'si Hydros.etude contient un Qs<0')"""
         if qlog is not None:
             qlog.put("Export HYDROS file")
         d50, sigma = float(bc.d50), float(bc.sigma)
-        lines = [f"{len(bc)}\n"] + [
+        data = [(t, qs) for t, qs in bc.data] or [(tinit, -1.0)]
+        lines = [f"{len(data)}\n"] + [
             f"{float(qs)!r} {float(t)!r} {d50!r} {sigma!r}\n"
-            for t, qs in bc.data
+            for t, qs in data
         ]
         self._write_parameters(repertory, f"hydros.{name}", lines)