--- a/artifacts/src/main/java/org/dive4elements/river/artifacts/sinfo/flowdepthdev/FlowDepthDevelopmentCalculation.java	Tue Apr 03 17:23:51 2018 +0200
+++ b/artifacts/src/main/java/org/dive4elements/river/artifacts/sinfo/flowdepthdev/FlowDepthDevelopmentCalculation.java	Thu Apr 05 11:57:54 2018 +0200
@@ -97,18 +97,26 @@
             return null;
 
         // FIXME: check current/hist wst have same discharge...
+        // FIXME: what means 'same discharge'
 
         final BedHeightInfo currentSoundingInfo = currentSounding.getInfo();
         final BedHeightInfo historicalSoundingInfo = historicalSounding.getInfo();
 
-        // final String label = createLabel(waterlevel, minBedHeight, maxBedHeight);
-
-        // final WKms wstKms = waterlevel.getWkms();
         final int currentWstYear = currentWaterlevel.getYear();
         final int historicalWstYear = historicalWaterlevel.getYear();
         final int currentSoundingYear = currentSoundingInfo.getYear();
         final int historicalSoundingYear = historicalSoundingInfo.getYear();
 
+        if (currentWstYear < 0) {
+            problems.addProblem("flowdepthdevelopmentcalculation.missingCurrentYear", currentWaterlevel.getName());
+            return null;
+        }
+
+        if (historicalWstYear < 0) {
+            problems.addProblem("flowdepthdevelopmentcalculation.missingHistoricalYear", historicalWaterlevel.getName());
+            return null;
+        }
+
         // FIXME: distinguish error messages
         FlowDepthUtils.checkYearDifference("", currentWstYear, currentSoundingYear, problems);
         FlowDepthUtils.checkYearDifference("", historicalWstYear, historicalSoundingYear, problems);
@@ -144,6 +152,10 @@
                 final double historicalWst = historicalWstProvider.getWaterlevel(station);
                 final double historicalBedHeight = historicalSounding.getMeanBedHeight(station);
 
+                /* ignore invalid lines */
+                if (Double.isNaN(currentWst) || Double.isNaN(currentBedHeight) || Double.isNaN(historicalWst) || Double.isNaN(historicalBedHeight))
+                    continue;
+
                 final double diffWst = (currentWst - historicalWst) * 100;
                 final double diffBedHeight = (currentBedHeight - historicalBedHeight) * 100;