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RAPID: WILDFIRE-INDUCED CHANGES TO FLUVIAL HYDRAULICS AND GEOMORPHOLOGY IN THE GRAND CANYON -THE 2025 DRAGON BRAVO FIRE BURNED MORE THAN 580 SQUARE KILOMETERS OF WATERSHEDS IN THE GRAND CANYON. AS A RESULT, LARGE VOLUMES OF COARSE SEDIMENT MAY BE DELIVERED TO THE COLORADO RIVER OVER THE COMING YEARS. THE BURNED AREAS ARE NOW HIGHLY SUSCEPTIBLE TO POST-FIRE FLASH FLOODS AND DEBRIS FLOWS. UPON REACHING THE RIVER, THE MATERIALS MOVED BY THESE EVENTS CAN FORM DEBRIS FANS THAT CONSTRICT THE RIVER CHANNEL, GENERATE RAPIDS, AND REORGANIZE SEDIMENT STORAGE. SUCH CHANGES IN THE NATURE OF THE RIVER THREATEN INFRASTRUCTURE, RIVER NAVIGABILITY, AND VISITOR AND BOATER SAFETY IN THE GRAND CANYON CORRIDOR. THE INCREASED LIKELIHOOD OF DEBRIS-FLOWS CREATES A UNIQUE OPPORTUNITY TO INVESTIGATE HIGH-ENERGY FLOW DYNAMICS IN A NATURAL, RAPIDLY EVOLVING SETTING. THE KNOWLEDGE GAINED FROM THIS PROJECT WILL HELP IMPROVE PREDICTION AND INFORM DECISION-MAKING IN FIRE-AFFECTED LANDSCAPES. IT WILL SUPPORT ASSESSMENT OF NAVIGATION HAZARDS, SEDIMENT IMPACTS, AND INFRASTRUCTURE VULNERABILITY. THE PROJECT ACTIVITIES WILL INCLUDE OUTREACH AND DATA-SHARING WITH LOCAL STAKEHOLDERS AND HANDS-ON SCIENTIFIC TRAINING FOR STUDENTS. DESPITE THEIR STRONG INFLUENCE ON RIVER MORPHODYNAMICS, THE HYDRAULICS OF FAN-RAPID COMPLEXES ARE SELDOM QUANTIFIED AT THE SPATIAL AND TEMPORAL RESOLUTION NEEDED TO UNDERSTAND HOW SUDDEN SEDIMENT INPUTS REORGANIZE FLOW. THE DRAGON BRAVO FIRE PROVIDES AN OPPORTUNITY TO ESTABLISH DETAILED HYDRAULIC AND GEOMORPHIC BASELINES AND EXAMINE HOW CHANNEL CONSTRICTION, HIGH-ENERGY FLOW, AND SEDIMENT DELIVERY SHAPE RAPIDLY VARIED FLOW PROFILES IN CONFINED CANYON SYSTEMS. THIS PROJECT WILL ADVANCE A THEORY-DRIVEN UNDERSTANDING OF RAPID MORPHOLOGY AND UNDULAR HYDRAULIC JUMPS BY LINKING DEBRIS-FAN GEOMETRY, SPECIFIC ENERGY DISTRIBUTION, AND FREE-SURFACE WAVE FIELDS ALONG THE COLORADO RIVER. BY EVALUATING HOW CONSTRICTION, HYDRAULIC ROUGHNESS, SLOPE, AND COHERENT FLOW STRUCTURE GOVERN THE EMERGENCE AND WAVELENGTH OF STATIONARY WAVES, THE PROJECT WILL TEST WHETHER SURFACE-WAVE PATTERNS RELIABLY DIAGNOSE UNDERLYING HYDRAULIC STATES IN STEEP RIVERS. THESE INSIGHTS WILL CLARIFY HOW EXTREME SEDIMENT INPUTS RESHAPE RAPIDS, SEDIMENT ROUTING, AND ENERGY GRADIENTS, STRENGTHENING BOTH FUNDAMENTAL HYDRAULIC THEORY AND APPLIED RIVER MANAGEMENT CAPABILITIES. THIS AWARD REFLECTS NSF'S STATUTORY MISSION AND HAS BEEN DEEMED WORTHY OF SUPPORT THROUGH EVALUATION USING THE FOUNDATION'S INTELLECTUAL MERIT AND BROADER IMPACTS REVIEW CRITERIA.- SUBAWARDS ARE NOT PLANNED FOR THIS AWARD.

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