Demonstration of a methodology for setting ecological flow and water level targets

Figures & data

Table 1. Steps of framework for ecological flows and water levels.

PHASE I
(Context setting)
(a)	Define subwatershed characteristics
(b)	Define subwatershed goals
(c)	Identify habitat specialists
(d)	Complete the functional analysis
(e)	Complete geomorphic/hydrologic classification and select analysis nodes
PHASE II
(Development of a reference regime and hydro-ecological analysis)
(a)	Characterize the natural regime
(b)	Assess the hydrologic alteration
(c)	Hypothesize ecological responses to hydrologic alteration
PHASE III
(Development of a target regime)
(a)	Set targets for overall ecosystem health
(b)	Set targets for ecological objectives
(c)	Integrate into a target regime

Figure 1 Lovers Creek subwatershed physical and biological characteristics.

Figure 2 Land cover within the contributing area of each analysis node. LOV, Lovers Creek sites; CWT, Central Western Tributary site.

Table 2. Translation of general goals to limiting needs (adapted from Al Zaghal 2010).

	Goals	Habitat Specialist	Required Functions
Biotic	maintain coldwater fish	brook trout	refugia from warm water
			connectivity to refugia
			spawning habitat
			connectivity to spawning habitat
	wetland protection	wetland amphibians	breeding habitat (vernal pools)
		wetland vegetation	soil saturation
Geomorphic	maintain geomorphic form and function	N/A	prevent excessive erosion
Human	allow for agricultural drain use	N/A	adequate field drainage

Table 3. Functional flow assessment for Lovers Creek streamflow points.

Goal type	Required functions	Variable(s) that limit the function	Flow-related process(es) governing variable	Flow regime (temporal aspects)	Non-flow related processes affecting variable
Biotic	maintain summer refugia from warm water	pool depth	flows capable of mobilizing accumulated superficial sediment to scour pools	spring	sediment yield
			adequate flows to maintain water depth	summer
			adequate flow depth to maintain temperature	summer	riparian cover, climate change, thermal discharges
		pool temperature	adequate amount of localized cool groundwater discharge to maintain pool temperature	summer
	maintain connectivity to thermal refuge areas	depth at riffle crest	adequate flows to maintain depth and velocity suitable for fish passage	summer	dams and barriers
	maintain spawning habitat	spawning substrate	flows that will flush fine sediment from spawning beds	early fall; brook trout spawn October-December (Scott and Crossman 1975)	sediment yield
		groundwater upwelling	adequate groundwater discharge to attract spawning brook trout	fall/winter	colmation of channel bed
	maintain connectivity to spawning habitat	depth at riffle crest	adequate flows to maintain depth and velocity suitable for fish passage	fall/winter	dams and barriers
Geomorphic	prevent excessive erosion	boundary shear stress	frequency and duration of erosive flows	all year	channel form and structure

Table 4. Basic streamflow statistics for all streamflow sites. LOV, Lovers Creek sites. CWT, Central Western Tributary.

	LOV1-01	LOV1-G	LOV1-03	CWT
Mean annual flow (m^3/s)	0.31	0.22	0.06	0
Period of record maximum (m^3/s)	36.2	21.6	5.6	1.4
Period of record minimum (m^3/s)	0.03	0.024	0.002	0

Figure 3 Median monthly flow and median monthly flow Coefficient of Dispersion (CD) for all study nodes. LOV, Lovers Creek sites.

Figure 4 Comparison of modelled pre-settlement and current hydrologic regime flow duration curves for site LOV1-01. LOV, Lovers Creek sites.

Figure 5 Ecological model describing flow magnitude and timing of important ecological functions for site LOV1-01. LOV, Lovers Creek sites.

Figure 6 Example calculation of the hydrologic alteration factor statistic, which is used as a target for overall ecosystem health.

Table 5. Table relating flow objectives to information required for quantification of flows.

Required functions	Important variable(s) that limit need	Flow-related process(es) governing variable	Flow regime (temporal aspects)	Flow quantification tool/method	Threshold calculation
maintain summer refugia from warm water	pool depth	flows capable of mobilizing accumulated superficial sediment to scour pools	spring	sediment entrainment equations	calculate flows capable of mobilizing accumulated superficial sediment in pools^∗
	pool depth	adequate flows to maintain water depth	summer	HEC-RAS	calculate flow to equal 50% pool and 50% riffle where the pool is at an adequate depth^∗∗∗
	pool temperature	adequate flow depth to maintain temperature	summer	HEC-RAS	calculate the flows to maintain a coldwater temperature class
	pool temperature	adequate amount of localized cool groundwater discharge to maintain pool temperature	summer	MIKE-SHE/FEFLOW	presence of groundwater discharge
maintain connectivity to thermal refuge areas	depth at riffle crest	adequate flows to maintain depth and velocity suitable for fish passage	summer	HEC-RAS	calculate flow to maintain adequate depth at riffle crest ^∗∗∗∗∗

^∗Al Zaghal 2010. ^∗∗Raleigh 1982. ^∗∗∗GRCA n.d.

Figure 7 An example of Environmental Flow Component (EFC) flow ranges. The horizontal lines on the hydrograph represent thresholds that separate each EFC.

Figure 8 The four types of ecological targets based on the direction of flow magnitude change and whether crossing the flow threshold is desired or not desired.

Table 6. Flow targets for ecological objectives. EFC, Environmental Flow Component.

EFC parameter	Flow regime (temporal aspects)	Ecological function(s)	Target type	Flow magnitude range (from EFC thresholds) (m^3/s)		Frequency and duration based on period of record natural hydrology Percentile
						25th	50th	75th
high flow (75^th percentile – 1.6 yr return interval)	all year	• Prevent excessive erosion	maximum threshold, exceedance not desired	0.24–7.5	frequency (times/year)	17	22	24
					duration (days)	2	2	2
high flow (75^th percentile – 1.6 yr return interval)	spring	• Scour pools to maintain pool depth for summer thermal refuge	minimum threshold, exceedance desired	0.24–7.5	frequency (times/season)	3	5	7
					duration (days)	2	2	4
low flow (50th percentile – 10^th percentile)	summer	• Maintain temperature and depth of summer pools	minimum threshold, non-exceedance desired	0.08–0.15	frequency (times/season)	7	8	11
		• Maintain connectivity to thermal refuge areas			duration (days)	5	7	12
	fall/winter	• Maintain connectivity to spawning habitat	minimum threshold, non-exceedance desired	0.08–0.15	frequency (times/ season)	4	6	8
					duration (days)	3	4	6
extreme low flow (10th percentile – 0^th percentile)	summer	• Maintain temperature and depth of summer pools	minimum threshold, non-exceedance desired	0.03–0.08	frequency (times/season)	0	2	5
		• Maintain connectivity to thermal refuge areas			duration (days)	2	4	7
	fall/winter	• Maintain connectivity to spawning habitat	minimum threshold, non-exceedance desired	0.03–0.08	frequency (times/season)	0	0	5-year return period
					duration (days)	3	5	6

Figure 9 Target flow regime for site LOV1-01. LOV, Lovers Creek sites

Al Zaghal, A. 2010. Ecological streamflows with geomorphic functions. Phd diss., University of Guelph.

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Raleigh, R.F. 1982. Habitat suitability index models: Brook trout. Fort Collins: US Fish and Wildlife Service.

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