diff --git a/src/Model/HydraulicStructures/Basic/Types.py b/src/Model/HydraulicStructures/Basic/Types.py
index d82998adf9d9df9147ef0c74114011a2074c2cbc..a976aaa37f7335a5a7e38ad49aab5c3518d5b904 100644
--- a/src/Model/HydraulicStructures/Basic/Types.py
+++ b/src/Model/HydraulicStructures/Basic/Types.py
@@ -35,3 +35,8 @@ class NotDefined(BasicHS):
             BHSValue("bar", float, 42.0),
             BHSValue("baz", int, 13),
         ]
+
+
+BHS_types = {
+    "ND": NotDefined,
+}
diff --git a/src/Model/HydraulicStructures/HydraulicStructures.py b/src/Model/HydraulicStructures/HydraulicStructures.py
index 5799925b8094206466f33792337b7a542c8e4e9a..6d1a4734b869cc29206fec4e20cb68cc19d5e509 100644
--- a/src/Model/HydraulicStructures/HydraulicStructures.py
+++ b/src/Model/HydraulicStructures/HydraulicStructures.py
@@ -233,6 +233,9 @@ class HydraulicStructure(SQLSubModel):
     def basic_structures(self):
         return self._data.copy()
 
+    def basic_structure(self, index: int):
+        return self._data[index]
+
     def add(self, index: int):
         value = NotDefined(status=self._status)
         self._data.insert(index, value)