Answer:
"debris-choked".
Step-by-step explanation:
In the given passage, the speaker/ author presents the difference between the Glen Canyon and Lake Powell. This contrasting image/ description is made in such a way that the difference is felt and projects a drastic image.
The comparison of these reservoirs is so drastic that the author uses life and death to compare it. While "Glen Canyon was alive. Lake Powell is a graveyard." And the one phrase that best contributes to the author's sad tone is "debris-choked", which presents an image of a place that is dying, or on the verge of death.