/**
 * Bit field layout of m5 for water tiles.
 */
enum WaterTileTypeBitLayout {
	WBL_TYPE_BEGIN        = 4,   ///< Start of the 'type' bitfield.
	WBL_TYPE_COUNT        = 4,   ///< Length of the 'type' bitfield.

	WBL_TYPE_NORMAL       = 0x0, ///< Clear water or coast ('type' bitfield).
	WBL_TYPE_LOCK         = 0x1, ///< Lock ('type' bitfield).
	WBL_TYPE_DEPOT        = 0x8, ///< Depot ('type' bitfield).

	WBL_COAST_FLAG        = 0,   ///< Flag for coast.
	WBL_RIVER_FLAG		  = 0,   ///< Flag for canal on river.

	WBL_LOCK_ORIENT_BEGIN = 0,   ///< Start of lock orientiation bitfield.
	WBL_LOCK_ORIENT_COUNT = 2,   ///< Length of lock orientiation bitfield.
	WBL_LOCK_PART_BEGIN   = 2,   ///< Start of lock part bitfield.
	WBL_LOCK_PART_COUNT   = 2,   ///< Length of lock part bitfield.

	WBL_DEPOT_PART        = 0,   ///< Depot part flag.
	WBL_DEPOT_AXIS        = 1,   ///< Depot axis flag.
};

......

enum CanalType {
	CANAL_NOT_RIVER = 0,	///< 
	CANAL_AND_RIVER = 1,	///< 
};


.....

static inline CanalType GetCanalType(TileIndex t)
{
	assert(HasTileWaterClass(t) && GetWaterClass(t) == WATER_CLASS_CANAL);
	return (CanalType)HasBit(_me[t].m6, WBL_RIVER_FLAG) ? CANAL_AND_RIVER : CANAL_NOT_RIVER;
}

static inline bool HasTileCanalOnRiver(TileIndex t)
{
	return HasTileWaterClass(t) && GetWaterClass(t) == WATER_CLASS_CANAL && GetCanalType(t) == CANAL_AND_RIVER;
}

static inline void SetCanalOnRiver(TileIndex t)
{
	assert(HasTileWaterClass(t) && GetWaterClass(t) == WATER_CLASS_CANAL);
	SB(_me[t].m6, 0, WBL_RIVER_FLAG, CANAL_AND_RIVER);
}