Add flood prediction tools: flood_depth, inundation, curve_number_runoff, travel_time (#923)

New xrspatial.flood module with four per-cell flood analysis functions
that build on the existing hydrology toolkit (HAND, flow_length, etc.):

- flood_depth: water depth from HAND raster and water level
- inundation: binary flood/no-flood mask
- curve_number_runoff: SCS/NRCS curve number runoff estimation
- travel_time: overland flow travel time via simplified Manning's equation

All four support numpy, cupy, dask, and dask+cupy backends.
Includes 45 tests covering known values, NaN propagation, edge cases,
input validation, and cross-backend equivalence.

Author: brendancol

xrspatial/__init__.py

@@ -15,6 +15,10 @@
 from xrspatial.curvature import curvature  # noqa
 from xrspatial.emerging_hotspots import emerging_hotspots  # noqa
 from xrspatial.fill import fill  # noqa
+from xrspatial.flood import curve_number_runoff  # noqa
+from xrspatial.flood import flood_depth  # noqa
+from xrspatial.flood import inundation  # noqa
+from xrspatial.flood import travel_time  # noqa
 from xrspatial.flow_accumulation import flow_accumulation  # noqa
 from xrspatial.flow_direction import flow_direction  # noqa
 from xrspatial.flow_direction_dinf import flow_direction_dinf  # noqa

xrspatial/accessor.py

@@ -115,6 +115,24 @@ def hand(self, flow_accum, elevation, **kwargs):
         from .hand import hand
         return hand(self._obj, flow_accum, elevation, **kwargs)
 
+    # ---- Flood ----
+
+    def flood_depth(self, water_level, **kwargs):
+        from .flood import flood_depth
+        return flood_depth(self._obj, water_level, **kwargs)
+
+    def inundation(self, water_level, **kwargs):
+        from .flood import inundation
+        return inundation(self._obj, water_level, **kwargs)
+
+    def curve_number_runoff(self, curve_number, **kwargs):
+        from .flood import curve_number_runoff
+        return curve_number_runoff(self._obj, curve_number, **kwargs)
+
+    def travel_time(self, slope_agg, mannings_n, **kwargs):
+        from .flood import travel_time
+        return travel_time(self._obj, slope_agg, mannings_n, **kwargs)
+
     def viewshed(self, x, y, **kwargs):
         from .viewshed import viewshed
         return viewshed(self._obj, x, y, **kwargs)
@@ -373,6 +391,24 @@ def hand(self, flow_accum, elevation, **kwargs):
         from .hand import hand
         return hand(self._obj, flow_accum, elevation, **kwargs)
 
+    # ---- Flood ----
+
+    def flood_depth(self, water_level, **kwargs):
+        from .flood import flood_depth
+        return flood_depth(self._obj, water_level, **kwargs)
+
+    def inundation(self, water_level, **kwargs):
+        from .flood import inundation
+        return inundation(self._obj, water_level, **kwargs)
+
+    def curve_number_runoff(self, curve_number, **kwargs):
+        from .flood import curve_number_runoff
+        return curve_number_runoff(self._obj, curve_number, **kwargs)
+
+    def travel_time(self, slope_agg, mannings_n, **kwargs):
+        from .flood import travel_time
+        return travel_time(self._obj, slope_agg, mannings_n, **kwargs)
+
     # ---- Classification ----
 
     def natural_breaks(self, **kwargs):