Sensitivity Analysis / Example Scenarios

A sensitivity analysis provides information on how sensitive a model is to individual parameters. This increases transparency and understanding of model outputs. One form of a sensitivity analysis is to provide example scenarios altering one variable at a time. In response to comments NOAA received from the Independent Peer Review of NOAA Fisheries’ Puget Sound Nearshore Calculator, the Nearshore Team developed these three example scenarios.

Scenario 1

Table 1 shows the habitat loss expressed as conservation debits for different overwater replacement structures under different Submerged Aquatic Vegetation (SAV) scenarios in the Lower Shore Zone (LSZ). The last column shows the influence of different SAV scenarios on the conservation debits as the relative percent increase compared to an SAV 0 scenario. The increase in debits for an SAV scenario of 3 compared to SAV scenario of 0 ranges between 36 and 41 percent depending on the type of structure.

Table 1: Effect of SAV Scenarios on Conservation Debits

ENTRY BLOCK: Replacement, Repair
Structure Element	Shore Zone	Quantity: Area/numbers	SAV	Conservation Debits	Percent Increase from SAV 0
Pier (GRATED)	LSZ	300 sf	0	-4.58	N/A
			1	-5.24	13%
			2	-5.88	28%
			3	-6.54	41%
Piles	LSZ	(2) 12"	0	-1	N/A
			1	-1.13	13%
			2	-1.25	25%
			3	-1.38	38%
Grated Float	LSZ	50 x 6, 300 sf	0	-23.27	N/A
			1	-26.08	12%
			2	-28.88	24%
			3	-31.7	36%
Solid Float	LSZ	50 x 6, 300 sf	0	-26.73	N/A
			1	-30.03	12%
			2	-33.34	25%
			3	-36.64	37%

Scenario 2

Table 2 shows the habitat loss expressed as conservation debits for an SAV scenario of 0 for different structures that can be assessed in the “Boat Ramp & Jetty” tab.

Table 2: Effect of Adjustment Factors on Conservation Debits

ENTRY BLOCK: Replacement, Repair			Adjustment Factors
Structure Element	Shore Zone	Quantity: Area	No Adj Factors	Natal Est = Yes (50%)	Pocket Est = Yes (30%)	Forage Fish = Yes (50%)	Drift Cell = Yes (20%)
Footings	USZ	50 x 6, 300 sf	-5.37	-8.06	-6.98	-8.06	-6.44
	LSZ	300	-5.97	-8.96	-7.76	-5.97	-5.97
	DSZ	300	-0.96	-1.44	-1.25	-0.96	-0.96
Jetty	USZ	50 x 6, 300 sf	-13.37	-20.06	-17.38	-20.06	-16.04
	LSZ	300	-11.54	-17.31	-15.00	-11.54	-11.54
	DSZ	300	-5.89	-8.84	-7.66	-5.89	-5.89
Boat Ramp	USZ	50 x 6, 300 sf	-8.48	-12.72	-11.02	-12.72	-10.18
	LSZ	300	-6.77	-10.16	-8.80	-6.77	-6.77
	DSZ	300	-1.43	-2.15	-1.86	-1.43	-1.43

Scenario 3

Table 3 shows the conservation debits associated with the installation of a new 100-foot vertical armoring in a South Central Puget Sound transport zone (slope = 0.295), where Mean Higher High Water (MHHW) is located at +9 feet and the Highest Astronomical Tide (HAT) is located at +11 feet; riparian conditions are trees/shrubs. No adjustment factors apply. These scenarios show how debits increase when the toe of the bulkhead is moved lower in the beach profile. In places where a bulkhead has to be constructed, moving the toe as high in the beach profile as possible is a good measure to minimize impacts.

Table 3: Bulkhead Scenarios; Effect of Toe Elevation on Conservation Debits.

Toe Elevation (ft)	MHHW (ft)	HAT (ft)	DSAYs	Conservation Debits*
11	9	11	-0.52	-52
10	9	11	-0.65	-65
8	9	11	-1.14	-114

* 1 DSAY = Conservation Debit/Credit * 100

Diagram showing the effect of the bulkhead toe elevation of a 100-foot-long new bulkhead on conservation debits — Figure 1. As the elevation of the toe of the bulkhead decreases, the impacts (conservation debits) increase.

Last updated by West Coast Regional Office on 10/10/2024