i

Decision Support Tool for Water Management and Environmental Flows:

Mill Creek Case Study

By

JENNY TA

B.S. (Massachusetts Institute of Technology) 2004

THESIS

Submitted in partial satisfaction of the requirements for the degree of

MASTER OF SCIENCE

in

Hydrologic Sciences

in the

OFFICE OF GRADUATE STUDIES

of the

UNIVERSITY OF CALIFORNIA

DAVIS

Approved:

____________________________________

Joshua H. Viers, Chair

____________________________________

Jay R. Lund

____________________________________

Samuel Sandoval-Solis

Committee in Charge

2015

ii

Table of Contents

List of Figures ............................................................................................................................... iii  

List of Tables ................................................................................................................................ v  

Acknowledgements ....................................................................................................................... vi  

Abstract ......................................................................................................................................... 1  

Introduction ................................................................................................................................... 3  

Mill Creek Case Study ................................................................................................................ 11  

Methods ...................................................................................................................................... 16  

Results ........................................................................................................................................ 25  

Discussion .................................................................................................................................. 39  

Conclusion .................................................................................................................................. 41  

References ................................................................................................................................. 42  

iii

List of Figures Figure 1. Map of Mill Creek watershed in Tehama County, California (elevation contour in

meters). ............................................................................................................................... 12  Figure 2. Map of lower reach of Mill Creek by the town of Los Molinos. ..................................... 13  Figure 3. Annual flows for water years 1999-2013 for upstream (MLM) and downstream (MCH)

stream gauges on lower Mill Creek. .................................................................................... 14  Figure 4. Difference in annual water volume between upstream and downstream gauges in lower

Mill Creek for water years 1999-2013 with Sacramento Valley Index water year types

indicated (C = critically dry, D = dry, BN = below normal, AN = above normal, W = wet). .. 14  Figure 5. Flow exceedance probabilities for upstream (MLM) and downstream (MCH) gauges for

water years 1999-2013. ...................................................................................................... 15  

Figure 6. Model schematic. ......................................................................................................... 16  Figure 7. Three environmental flow cases: a seasonal fall and spring fish passage flow, a 2.55

cms minimum instream flow, and an 80% sustainability boundary flow. ............................ 23  

Figure 8. Modeled and observed lower Mill Creek outflow for water year 2008 with baseline water

management (NSE = 0.92). ................................................................................................ 26  Figure 9. Fish passage environmental flow allocations and total water diversions for water year

2008 with baseline water management. ............................................................................. 27  Figure 10. Fish passage environmental flow shortages for critically dry water year 2008 with

baseline water management. .............................................................................................. 28  

Figure 11. Fish passage shortages for critically dry (2008), below normal (2010), and wet (2006)

water year types for five water management alternatives: baseline, 4 wells, water

agreement, water agreement and 4 wells, and leaving Droz and Orange Cove instream. The

x-axis corresponds to water year weeks and the y-axis correspond to water volume

shortages in mcm. ............................................................................................................... 29  Figure 12. Percent change of fish passage flow shortages for different water management

alternatives compared to baseline for critically dry water year 2008. ................................. 30  Figure 13. Percent change of fish passage flow shortages for different water management

alternatives compared to baseline for below normal water year 2010. ............................... 31  

Figure 14. Percent change of fish passage flow shortages for different water management

alternatives compared to baseline for wet water year 2006. ............................................... 32  

iv

Figure 15. Minimum instream flow shortages for critically dry (2008), below normal (2010), and

wet (2006) water years for baseline, 4 wells, water exchange agreement, agreement and 4

wells, Droz and Orange Cove left instream, and LMMWC water left instream. The x-axis

corresponds to water year weeks and the y-axis corresponds to water volume shortages in

mcm. ................................................................................................................................... 34  

Figure 16. Percent change of minimum instream flow shortages for different water management

alternatives compared to baseline for critically dry water year 2008. ................................. 35  Figure 17. SBA environmental shortages for critically dry (2008), below normal (2010), and wet

(2006) water years for baseline, 4 wells, agreement, agreement and 4 wells, Droz and

Orange Cove purchase, and LMMWC purchase management options. The x-axis is in water

year weeks and the y-axis is water volume shortages in mcm. .......................................... 36  

v

List of Tables Table 1. Model inputs, example variable values, data types, and sources. ................................ 19  

Table 2. Description of different water management options used in model runs. ..................... 24  Table 3. Annual volume of shortages for fish passage, MIF, and SBA environmental flow cases

by water year type and water management alternatives. Percent decrease in environmental

flow shortage from baseline indicated in parentheses. ....................................................... 38  

vi

Acknowledgements

I would like to acknowledge the financial support for this research from the UC Davis Center for

Watershed Sciences, The Nature Conservancy, and the UC Davis Hydrologic Sciences

Graduate Group Fellowship. Rodd Kelsey, Gregg Werner, and Jeanette Howard of The Nature

Conservancy provided valuable insight on the Mill Creek watershed essential to developing a

representative model. Countless members of the Shed provided valuable feedback and

discussion, in particular members of Professor Jay Lund’s Water Systems Research group.

Special thanks are extended to my advisor Josh Viers and committee members Jay Lund and

Sam Sandoval for their invaluable encouragement and support. Finally, thanks to my family and

Albert for everything.

1

Jenny Ta

June 2015

Hydrologic Sciences

Abstract

Stream flow drives many physical and ecological processes in rivers that support freshwater

ecosystems. Human activities like dam operations, water diversions, and flood control

infrastructure together have fundamentally altered many streams. Water scarcity from increasing

water demands and prolonged droughts has further stressed freshwater ecosystems, which in

turn is prompting the development of new methods and tools for establishing environmental

flows. This study developed a linear programming model for exploring the effects of water

management alternatives on environmental flows in river systems that have minimal or no

regulation from dam operations, but still have altered flow regimes due to surface water

diversions. The model was applied to a case study on Mill Creek, a tributary of the Sacramento

River in northern California’s Tehama County, whose altered flow regime affects fall and spring

fish migration to upstream spawning habitat. Test cases were used to examine how water

management alternatives can improve environmental flow allocations while striving to meet

agricultural water supply demands. These test cases included: 1) fish passage flows for

California Central Valley Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout

(Oncorhynchus mykiss); 2) a 2.55 cms minimum instream flow (MIF); and 3) a sustainability

boundary approach (SBA) with a flow target of 80% of natural flow. The model quantifies the

effect of water management alternatives such as conjunctive use, water rights transfers, and

water exchange agreements on instream environmental flow conditions. The model identified the

2

last two weeks of October as a consistent period of shortage for fall fish passage flows during all

water year types from critically dry to wet water years. Shortages to fish passage flows could be

eliminated through the combined use of a water exchange agreement and conjunctive use wells.

The MIF and SBA environmental flow cases both required acquisition of the largest water right

holder in the system to decrease environmental shortages by over 80%. This modeling approach

can be applied to other river systems as a decision-support tool for conservation organizations

and government agencies to make more informed decisions regarding management of scarce

water resources to maximize ecological function while minimizing impact on human uses of

water.

3

Introduction

Rivers carry only 0.0002 percent of water globally (Shiklomanov 1993), but support 6 percent of

biodiversity that has been discovered (Dudgeon, Arthington et al. 2006). However, flows in rivers

have been transformed due to their usefulness to society. Dams built to harness the power of a

river interrupt its flow and sever its tie to natural rainfall and runoff, allowing humans to dictate

river flow. Water diversions siphon volumes of water from rivers to supply water, sometimes

leaving rivers trickling or dry.

Human activities like dam operations, water diversions, and flood control infrastructure have

impacts beyond biodiversity, as rivers provide critical ecosystem services that human societies

depend on (Dudgeon 2010, Arthington 2012). For example, the rich diversity of species in

freshwater ecosystems supports economic productivity such as fisheries. They are also a

valuable source of genetic information and promote cleaning of water (Dudgeon, Arthington et al.

2006). Biologically complex and functionally intact freshwater ecosystems provide goods and

services like food supply, purification of industrial and human wastes, flood control, and plant and

animal habitats and also contribute to adaptive capacity to future environmental alterations like

climate change (Baron, Poff et al. 2002). Since biodiversity declines are greater in freshwater

ecosystems than in most terrestrial ecosystems, it can be said that freshwater ecosystems are

the most endangered ecosystems in the world (Sala, Chapin III et al. 2000). For these reasons,

there is an urgent need for sustainable water resource allocation to maintain the processes that

support freshwater ecosystem integrity.

4

Natural Flow Regime Paradigm

The ecological integrity of riverine ecosystems depends on the natural dynamic character of

streamflow captured by five components of flow regime: magnitude, frequency, duration, timing,

and rates of change. Thus, streamflow has been identified as a master variable that controls

physical and ecological processes in rivers (Poff, Allan et al. 1997), and its regulation is

increasingly important for environmental management. For instance, high magnitude flows

create disturbance through scour and provide sediments which initiate succession in riparian

forests (Rood, Samuelson et al. 2005). In addition, reproductive success of riparian and riverine

species such as cottonwood (Populus spp.) and the foothill yellow-legged frog (Rana boylii)

depend on the timing and rate of change of the spring snowmelt recession of

Mediterranean-montane streams (Yarnell, Viers et al. 2010). However, modifications of a river’s

natural flow regime such as from the construction of dams for hydroelectric power and water

supply have negatively impacted aquatic species that have evolved to depend on a river’s natural

flow. Altered flow regimes have been shown to affect aquatic biodiversity in streams and rivers

(Bunn and Arthington 2002) and have also been linked to changes in human well-being (Naiman

and Dudgeon 2011). Even small spatially distributed reservoirs affect river flow (Deitch, A.M. et

al. 2013). Accelerating degradation of freshwater ecosystems (Dudgeon, Arthington et al. 2006)

due to human water use threaten both human water security and river biodiversity (Vorosmarty,

McIntyre et al. 2010). For freshwater conservation to be viable for the long-term, water

management must make compromises between human livelihoods, biodiversity conservation,

and ecosystem function. Thus, there is growing recognition of the need to conserve freshwater

5

ecosystems and biodiversity through identifying and allocating environmental flows.

Environmental Flow Science

Environmental flows characterize the quantity, timing, and quality of water in rivers required to

sustain freshwater or estuarine ecosystems and the human well-being that relies on these

ecosystems (Brisbane Declaration 2007). Several approaches to developing environmental flow

requirements exist from the most basic minimum instream flows, to statistical Tennant Methods,

ELOHA, percent change from natural flow (SBA), and hydraulic modeling approaches (Tharme

2003). One approach to environmental flows is to limit the extent of alteration to a natural flow

regime or to design flow regimes for specific ecological functions in regulated rivers (Acreman,

Arthington et al. 2014).

While some studies focus on water abstraction restrictions (Acreman, Dunbar et al. 2008) and

the effect of small-scale spatially distributed water reservoirs (Deitch, A.M. et al. 2013), most

environmental flow studies focus on reservoir re-operation of large centralized water

management systems (Richter and Thomas 2007, Yin, Yang et al. 2011, Shiau and Wu 2013,

Jager 2014). An example of reservoir re-operation for environmental flows was the

implementation of dam operation requirements on Putah Creek to restore specific flow

requirements to support native fish (Kiernan, Moyle et al. 2012). Kiernan et al found that following

implementation of a design flow that mimicked natural early spring pulse flows increased the

proportion of native fish species in reaches previously dominated by alien fish species.

6

Though there has been a lack of studies and development of tools to facilitate allocation of

environmental flows in diversion-impacted rivers, a landmark 1983 California Supreme Court

case set precedent for preserving natural environmental capital by invoking the public-trust

doctrine (Dunning 1989). In this case, the City of Los Angeles Department of Water and Power

was obligated to protect Mono Lake’s ecosystem by reducing water supply diversions to

preserve environmental flows (Koehler 1995).

Growing water demands and global climate change has exacerbated the uncertainty of water

availability and conflict among water users. From 2012 to the time of publication of this paper,

California is experiencing a major drought (Swain, Tsiang et al. 2014), forcing difficult decisions

regarding the allocation of water, such as mandatory reduction of diversions from rivers to

provide minimum flows for state and federally-listed anadromous fish (CA State Water

Resources Control Board 2015). An uncertain and scarce water supply coupled with competing

water demands calls for tools that enable people to make better management decisions. This

research addresses water scarcity in diversion-impacted rivers using a decision-support tool to

explore water management alternatives to meet agricultural water supply needs while striving for

maximum support of freshwater ecosystems.

7

The model developed in this study explored the following research questions:

1. Given a specific environmental flow target, represented as a design hydrograph in a river

subject to water abstractions, when and to what extent is there insufficient water to meet

environmental flow demands?

2. What are the effects of different water management alternatives on instream environmental

flow?

3. How do water management alternatives perform in different water year types?

Water transfers are an emerging management tool for acquiring water to support freshwater

ecosystems. To make informed decisions on financial investments in water transfers for the

environment, it is necessary to understand when water transfers would be needed and the

volume needing to be transferred. The first question explored in this study aims to quantify when

and by how much environmental flow targets are not met. A combination of water management

alternatives may be needed to acquire enough water for environmental flow. For this reason, it is

useful for decision makers to understand how different water management options will reduce

environmental flow shortages. In addition, water management alternatives for meeting

environmental flow targets may change between wet and dry years. For this reason, this study

also explores the effect of different water management alternatives during different water year

types as defined by the Sacramento Valley Index (DWR 2013).

8

Central Valley Chinook Salmon and Steelhead Trout

Life history requirements for Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout

(Oncorhynchus mykiss) were used as test cases to explore how different water management

alternatives can improve environmental flow objectives while minimizing impact to local

agricultural water supply, as environmental flow requirements aimed at protecting broad-based

ecological function are increasingly being used to manage these freshwater species as both are

threatened species (Central Valley spring-run Chinook salmon are listed as threatened in the

state and federal Endangered Species Acts and the California Central Valley steelhead trout are

listed a threatened in the federal Endangered Species Act (CA Department of Fish and Wildlife

2015)).

Pacific salmon have important cultural, ecological, and economic value throughout their range.

Ecologically, salmon are a keystone species, transporting productivity from the ocean into

terrestrial systems (Gende, Edwards et al. 2002). Nutrients brought inland by salmon are found

in terrestrial food chains in species from eagles to riparian vegetation (Cederholm, Kunze et al.

1999). They are born and reared in freshwater streams, then migrate to the ocean to mature, and

finally returning to their native freshwater stream years later to spawn. While most salmon

migrate relatively short distances to spawn (less than 150 km), some can migrate more than

2,000 km to spawning habitat, such as in the Yukon River in Alaska (Moyle 2002). These focal

species, like all anadromous Pacific salmon, have been harmed by myriad effects of global

environmental change, including direct human effects on river ecosystems.

9

Salmon migrate approximately 450 km from the San Francisco Bay, up the Sacramento River to

spawning habitat on Mill Creek (Tehama County, CA), one of the highest known spawning

elevation for Pacific salmon at 1,800 meters (Moyle 2002). Mill Creek contains spawning habitat

for spring and fall-run Chinook salmon and steelhead trout. Spring and fall-run species are two of

four major Central Valley runs (fall, late-fall, winter, spring) of distinct populations within the

species that exhibit genetically-based adaptations to regional environments. Central Valley

Chinook salmon are categorized into two basic life history types: ocean-type and stream-type.

The juveniles of ocean-type fish spend a short amount of time (3-12 months) rearing in

freshwater and spawn soon after entering freshwater as adults returning from the ocean. In

contrast, stream-type juvenile fish spend over a year rearing in freshwater and return to

freshwater streams from the ocean before reaching full maturity (Moyle 2002).

The Central Valley spring-run evolutionary significant unit (ESU) includes populations in the

Sacramento and San Joaquin River, though the San Joaquin spring-run has become extinct

(Moyle 2002). While spring-run Chinook salmon (SRCS) were once the most abundant in the

Central Valley, populations have declined to the point where only remnant populations remain in

Butte, Mill, Deer, and Antelope Creeks (DFW, 1998). These remaining headwater habitats were

historically minor habitats for the once abundant SRCS (Moyle 2002), whose spawning grounds

were blocked by the construction of dams on many Sacramento tributaries.

10

SRCS have a classic stream-type life history pattern. They enter the Sacramento River as

immature fish from late-March through September, migrate as far upstream as possible, then

hold over in deep, cold-water pools over the summer. Spawning occurs in early fall (mid-August

through early-October). Juveniles emerge in November through March, rearing in streams from 3

to 15 months. Outmigration of juvenile salmon occurs during all months in the Sacramento River

in various sizes (from fry to smolts), with peak outmigrations occurring in winter (Jan-Feb) and

then again in spring (April) (Moyle 2002). Mill Creek, the case study developed in this research,

is seasonally dewatered in the summer low flow season, impairing this seasonal fish migration.

11

Mill Creek Case Study

Mill Creek, in Tehama County, California, runs approximately 95 kilometers from the peak of

Mount Lassen to the Sacramento River, draining 342 km2 of watershed (Figure 1). Due in part to

its rugged terrain, the higher elevation reaches (> 1000 m) of this river have remained largely

undisturbed by human development and still support holding and spawning habitat for spring-run

Chinook salmon and steelhead (Palmer 2012). In the lower gradient reach flows, prior to flowing

through the unincorporated town of Los Molinos and reaching its confluence with the Sacramento

River, Mill Creek is subject to several water diversions. The irrigation season is April 1st to

October 31st, during which water is withdrawn from the lower reaches of Mill Creek at two

diversions for agricultural users in the Los Molinos area to irrigate orchards and pastureland. Two

stream gauges are in the lower Mill Creek reach (Figure 2), an upstream gauge (USGS

11382500, hereafter referred to with CDEC code MLM standing for Mill at Los Molinos) and a

downstream gauge (DWR A004420, hereafter referred to with CDEC code MCH for Mill Creek at

Highway 99). Two diversions, the Upper Diversion Dam and Warn Dam, are operated by the Los

Molinos Mutual Water Company with a combined diversion capacity of 150 cfs (G. Werner,

personal communication, January 17, 2015). Since the watershed is fully allocated, diversions

from these two points during the irrigation season have can dewater the lower reaches of Mill

Creek during summer low flows. In an effort to restore summer in-stream flows, an Interagency

Water Exchange Agreement has been created to exchange groundwater pumping for irrigation in

return for decreases in surface water diversions during fish migration seasons (Heiman and

Knecht 2010).

12

Figure 1. Map of Mill Creek watershed in Tehama County, California (elevation contour in meters).

Water rights on Mill Creek were fully adjudicated by the state in the 1920s (Superior Court of

Tehama County 1920). Flows up to 5.7 cms (203 cfs) are allocated to water users, which covers

most, if not all, summer base flow in Mill Creek. Since the entire river flow is allocated from 5.7

cms (203 cfs) and below, diversions during the low flow season lead to dewatering of the river

downstream of Ward Dam, impairing migration of spring and fall-run Chinook salmon

(Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss).

13

Figure 2. Map of lower reach of Mill Creek by the town of Los Molinos.

During the irrigation season from April 1st to October 31st, flows in lower Mill Creek can be

dewatered. Figure 3 shows annual flows for both gauges for water years 1999 to 2013. There is a

38 to 70 mcm (31,000 to 57,000 acre-feet) annual difference in water volume between the

upstream and downstream gauges (Figure 4).

!(

!(

!

!

0 1.5 30.75 Kilometers

Mill Creek

¯

Mill Creek Watershed

Sacramento River

MLM gauge

MCH gauge

Ward Dam

Upper Diversion Dam

14

Figure 3. Annual flows for water years 1999-2013 for upstream (MLM) and downstream (MCH) stream

gauges on lower Mill Creek.

Figure 4. Difference in annual water volume between upstream and downstream gauges in lower Mill

Creek for water years 1999-2013 with Sacramento Valley Index water year types indicated (C = critically

dry, D = dry, BN = below normal, AN = above normal, W = wet).

15

Flow exceedance probabilities (Figure 5) were computed with available data for the period of

record for the two stream gauges. This period of record is restricted by the downstream MCH

stream gauge which only has data available for water years 1999 through 2013. The impact of

diversions during the irrigation season can be seen in the low exceedance discharges on the

downstream gauge.

Figure 5. Flow exceedance probabilities for upstream (MLM) and downstream (MCH) gauges for water

years 1999-2013.

16

Methods

A linear programming model of the Mill Creek case study was developed to examine

environmental flow cases and simulate water management alternatives. The model represents

the lower Mill Creek river reach, which is subject to multiple diversions and an evolving

environmental flow requirement. Figure 6 shows a schematic of the Mill Creek environmental flow

model with two diversions, A1,t and A2,t , each representing individual water users with diversion

demands that change with time. Inflow into the reach of interest is represented by It.

Figure 6. Model schematic.

Environmental flow allocation, AE,t, is represented as a water user in the system with flow

requirements downstream of all diversions. Water diverted from the river is transported through

canals to agricultural users, most of which are outside the Mill Creek watershed boundary. For

this reason, the model assumes no return flows to Mill Creek from water users. The model also

assumes negligible stream accretion. Outflow, , at the downstream end of the river reach, is

calculated from the following water balance,

It

Ot

A1,t

A2,t

AE,t

Ot

17

where is each water diverter in the system, and 𝑛 is the total number of water diverters in the

system. Environmental flow allocations are not included in the water balance equation because

they represent water that stays in the river and is a component of outflow.

Each water user has a time dependent water demand, represented by Di,t. Environmental flow

demand is represented by DE,t, which is determined by a design hydrograph developed for

specific environmental flow requirements. All water users, including the environmental user, are

assigned a shortage penalty coefficient, , that reflects water right priority. Decision variables

are allocations to all water users, both human and environmental demands. The objective

function minimizes the sum of the penalty-weighted shortages, as follows.

Minimize:

Subject to:

No negative diversions.

Diversions cannot exceed water demand.

No negative outflow.

Inflow must be greater than or equal to sum of allocations

i

p

Z =nX

i

Pi,t (Di,t �Ai,t) +X

PE,t (DE,t �AE,t)

18

The linear programming model was implemented in Microsoft Excel 2010 with the OpenSolver

2.6 add-in1. The model inputs required are upstream inflow discharge, downstream outflow

discharge, water diversion demands in the system, and a desired time-series hydrograph

representing the environmental flow target of interest (Table 1). Modeled decisions that can vary

to represent different water management options are the irrigation periods for each water right

holder, the option to purchase and leave instream individual water rights, and the number,

pumping capacity, and use of conjunctive use wells.

1 http://opensolver.org/installing-opensolver/

19

Table 1. Model inputs, example variable values, data types, and sources.

Model Validation

Water inflow values into lower Mill Creek were taken from USGS (11381500) stream gauge

readings. A 1920 Tehama County Superior Court decree designated a table that defines water

rights for all water users in the system based on the amount of water in Mill Creek from 5.75 cms

and below (Superior Court of Tehama County 1920). The model uses these water right values for

each water user and assumes that these amounts will be diverted from the river and taken as

water demand input for the model. Although not all water users will divert the entire amount of

their water right, this conservative approach to modeling diversion amounts much can help

Inputs Example Variable Values Data Type SourceInflow stream gauge data time series (csv file) USGS; CDEC

(weekly time step)water year types:

critically dry string Sacramento dry Valley Index

below normalabove normal

wet

Water Rights weekly diversion rate (cfs) numeric float 1920 Tehama (Irrigation Demand) Court Decree

Environmental Flow Target seasonal fish passage flows discharge time series 2014 DFW, NMFSminimum instream flows (weekly time step) Drought Agreementpercentage of full natural flowfunctional flows

Priority Ranking of Users Shift priority of environmental user integer 1920 Tehama 1 = highest priority Court Decree

Water Management OptionsIrrigation Period April 1 to October 31 boolean user defined

shifting periods of diversion 1 = irrigated0 = not irrigated

Groundwater Wells number of wells numeric integer user definedwell capacity numeric float

Water Exchange Agreements instream environmental flow boolean user definedTNC water rights available for irrigation numeric float

Individual Water Rights leave instream or divert boolean user defined

20

guarantee flows for instream environmental purposes. These water demands were then used as

input in the model to simulate river flow for five representative water year types defined by the

Sacramento Valley Water Year Index as defined by the California Department of Water

Resources (DWR 2013).

Model testing was conducted by comparing simulated outflows with observed discharge at the

downstream DWR MCH gauge through the calculation of Nash-Sutcliffe efficiencies (NSE). NSE

were computed with the following equation (Moriasi, Arnold et al. 2007):

where is the i-th observation of discharge at the DWR MCH gauge, is the i-th

simulated value, is the mean value of observed discharge, and n is the total number of

observations.

NSE = 1�" P

n

i=1

�Y obs

i

� Y sim

i

�2P

n

i=1

�Y obs

i

� Y mean

�2

#

Y obs

i

Y simi

Y mean

21

Environmental Flow Targets

Figure 7 illustrates three environmental flow cases run in the model:

1. A design hydrograph representing target environmental flow for minimum fish passage flows

was created based on minimum flow requirements set during 2014 Volunteer Drought

Agreements between the National Marine Fisheries Service and the California Department of

Fish and Game and water rights holders on Mill Creek in Tehama County (Howard 2014). Spring

base flows of 1.42 cubic meters per second (cms) from April 1st to June 14th are required for adult

SRCS and juvenile SRCS and steelhead followed by 0.71 cms from June 15th to June 30th for

juvenile SRCS and steelhead. In the fall, base flows of 1.42 cms are required for out-migrating

juvenile SRCS and steelhead and upstream migration of adult steelhead from October 15th to

December 31st. Pulse flows to attract upstream migration of adult SRCS are needed to mimic the

natural increases in stream flow due to spring precipitation and snowmelt. From April 15th to June

14th, a minimum pulse flow of 1.42 cms greater than the base flow is required for a minimum of

24 hours once every two weeks. Since the model uses a weekly time step, the 24 pulse flows

recommended to cue migration were included in the design hydrograph by calculating the

corresponding volume of water needed for each pulse flow and adding that volume to the weekly

flow demand. These flow requirements provide the minimum flows needed for migration of adult

and juvenile fish in lower Mill Creek below Ward Dam.

2. A second environmental flow case was based on preliminary recommendations from the

22

Central Valley Freshwater Needs Assessment conducted by The Nature Conservancy that

analyzed stream gauge data from the upstream Mill Creek MLM gauge using the Indicators of

Hydrologic Alteration (IHA) software (Richter, Baumgartner et al. 1996). This study indicated that

a minimum instream flow of 2.55 cms would be ideal for supporting a suite of freshwater focal

species such as cottonwood (Populus sp.), freshwater mussels (Margaritifera falcata), western

pond turtle (Actinemys marmorata), bank swallow (Riparia riparia), as well as Chinook salmon

and steelhead and resident native fish.

3. A third environmental flow case was based on the concept of a sustainability boundary limit

that defines the extent of tolerable hydrologic alteration in the system (Postel and Richter 2003).

80% of full natural flow was chosen as a representation of a sustainability boundary

environmental flow target for the purposes of running the model. However, a real-life

implementation of the sustainability boundary approach (SBA) require management goals set by

water managers in collaboration with local stakeholders.

23

Figure 7. Three environmental flow cases: a seasonal fall and spring fish passage flow, a 2.55 cms

minimum instream flow, and an 80% sustainability boundary flow.

Model Runs

Each environmental flow case was run with a selection of water management alternatives (Table

2). One water management option expands the use of pumping groundwater to meet water

supply demands thereby allowing more water to be left instream to meet environmental flow

requirements. Two wells are currently available with a combined capacity of 0.28 cms. Based on

this information, potential new wells were represented with individual capacities of 0.14 cms in

the simulation model. Another water management option was to purchase water rights from

individual users in the system and leave the water instream to meet environmental flow

requirements. Of the eleven water right holders in the system, the Droz and Orange Cove rights

have been under consideration for potential water exchange or transfer negotiations and where

24

therefore chosen to be simulated in the model as potential water transfers. The Los Molinos

Mutual Water Company (LMMWC) rights have the largest percent (68%) of water rights in the

system and was selected as a water transfer option in the simulation to quantify its effect on

meeting the MIF and SBA cases as these required the largest volume of water. A third

management option is a water exchange between The Nature Conservancy (TNC) and LMMWC

in which existing TNC water rights would be available for diversion between July 1st and October

14th. In return, LMMWC would leave 0.68 cms (24 cfs) instream after October 15th for

approximately three weeks to supplement the TNC instream flows for fall fish passage through

lower Mill Creek.

Table 2. Description of different water management options used in model runs.

Each environmental flow case and water management alternative were run with representative

water year types based on the California Department of Water Resources Sacramento Valley

Index (DWR 2013). The following representative water year types were selected for model runs:

critically dry (2008), dry (2009), below normal (2010), above normal (2005), and wet (2006).

Water Management Option DescriptionBaseline Irrigation period for all water users from April 1 to October 31

TNC water rights left instream year round

Groundwater Wells 4 wells each with a pumping capacity of 5 cfs (0.14 cms)

Water Exchange AgreementTNC water rights diverted from July 1 to October 14, left instream otherwiseSupplemental instream flows of 24 cfs for 3 weeks (October 15 to early November)

Water Rights Purchase Purchase of water rights to leave instreamDroz, Orange Cove, Los Molinos Mutual Water Company (LMMWC)

Combination Combined 4 wells and water exchange agreement

25

Results

The model identified periods of water scarcity, quantified water shortages to each of the three

environmental flow cases, and explored the effects of different water management alternatives

on improving instream flows. To address these particular questions, the environmental water use

was assigned the lowest priority to ensure that agricultural water users are allocated water prior

to instream flow. Model testing of predictive accuracy with NSE values described previously were

calculated for baseline model runs for each water year type. A NSE value of 1 indicates a perfect

match between modeled and observed discharge. The following NSE values were calculated for

each water year type with water year in parentheses: Critically Dry (2008), NSE = 0.92; Dry

(2009), NSE = 0.96; Below Normal (2010), NSE = 0.87; Above Normal (2005), NSE = 0.86; Wet

(2006), NSE = 0.96.

Figure 8 shows modeled outflow in lower Mill Creek for the critically dry water year 2008 with

baseline water management. The modeled flow regime remains nearly unaltered during the

winter and diminishes starting on April 1st (week 27) till October 31st (week 5) corresponding to

the irrigation season. Observed outflows at the DWR MCH stream gauge show a similar pattern

of winter season unaltered flow with noticeable surface water abstractions starting on April 1st

and ending in mid-October (week 3) (Figure 8).

26

Figure 8. Modeled and observed lower Mill Creek outflow for water year 2008 with baseline water

management (NSE = 0.92).

Fish Passage Case

The fish passage case was intended to provide flows at critical times of year. Figure 9 shows

water allocation to environmental fish passage flows for critically dry water year 2008. During the

fall, October 15th through the first week of November, water year weeks 3 to 5 have insufficient

water to meet upstream migration passage flow requirements after agricultural diversions.

Similar conditions exist in the spring, where weeks 36 through 39 (approximately June 9th to 29th)

have insufficient water for spring-run Chinook salmon and steelhead trout downstream

outmigration.

27

Figure 9. Fish passage environmental flow allocations and total water diversions for water year 2008 with

baseline water management.

Over the critically dry water year 2008, total annual water shortage to fish passage flow

requirements is 3.0 million cubic meters (mcm), roughly 2400 acre-feet (Figure 10). The

shortages to fish passage flows occur in two main periods: 2.1 mcm (1700 acre-feet) during the

fall and 0.9 mcm (700 acre-feet) in the spring. The fall shortage volume of 2.1 mcm (1700

acre-feet) was also found for below the normal water year and decreased to 1.7 mcm (1400

acre-feet) for the wet water year.

28

Figure 10. Fish passage environmental flow shortages for critically dry water year 2008 with baseline water

management.

Figure 11 shows fish passage flows water shortages for three different water year types

(critically dry, below normal, and wet) and the different water management alternatives (baseline,

4 conjunctive use wells, water exchange agreement, a combination of wells and water exchange

agreement, and water rights purchases). Annual environmental shortage drops from 3.0 mcm

(2400 acre-feet) in critically dry water year 2008 to 2.1 mcm (1700 acre-feet) in below normal

water year 2010 and 2.0 mcm (1600 acre-feet) in wet water year 2006. The model indicates

water shortage for fall fish passage flows during the last two weeks of October and the first week

of November for all water year types from critically dry to wet for baseline water management.

The spring shortages during weeks 36 to 39 present in critically dry water year 2008 are not

present in the below normal and wet water years.

29

Figure 11. Fish passage shortages for critically dry (2008), below normal (2010), and wet (2006) water

year types for five water management alternatives: baseline, 4 wells, water agreement, water agreement

and 4 wells, and leaving Droz and Orange Cove instream. The x-axis corresponds to water year weeks

and the y-axis correspond to water volume shortages in mcm.

30

Figure 12 shows the percentage decrease in fish passage flow shortages for the four water

management options compared to baseline during critically dry water year 2008. The Droz and

Orange Cove water transfer has the smallest reduction in annual environmental shortage of

31%. The four conjunctive use wells reduced annual shortage by 61%, while the water exchange

agreement had a reduction of 41% from baseline. When only considering the fall fish passage

period, the exchange agreement reduces shortages by about 60% compared to about 50% for

the four wells. Finally, the combination of four wells and water exchange agreement nearly

eliminated total annual water shortage. This alternative resulted in a shortage of 0.2 mcm (160

acre-feet) compared to the 3.0 mcm (2400 acre-feet) baseline shortage, with a reduction of 94%.

Figure 12. Percent change of fish passage flow shortages for different water management alternatives

compared to baseline for critically dry water year 2008.

Below normal water year 2010 and wet water year 2006 both only showed shortages during the

fall passage season and had similar reductions in shortages from each management alternative.

31

For the below normal water year, the Droz and Orange Cove water transfer reduced shortages

by 16%, the four wells 50%, the exchange agreement 60%, with the well and exchange

agreement combination reducing 100% of shortages (fFigure 13). In the wet water year, the

management alternatives performed similarly with the following shortage reductions: Droz and

Orange Cove (18.2%), four wells (52%), exchange agreement (62%), and elimination of all

shortages with the wells and exchange agreement combination (Figure 14).

Figure 13. Percent change of fish passage flow shortages for different water management alternatives

compared to baseline for below normal water year 2010.

32

Figure 14. Percent change of fish passage flow shortages for different water management alternatives

compared to baseline for wet water year 2006.

Minimum Instream Flow Case

A minimum instream flow of 2.55 cms (90 cfs) was run in the model to see how water

management actions can improve a more broad-based environmental flow requirement to

support a set of focal freshwater species in addition to anadromous salmonids. Figure 15 shows

results of model runs with the same water management alternatives explored above with an

additional water rights purchase of LMMWC water rights. The baseline condition experiences an

annual shortage of 30.9 mcm (25,000 af) for critically dry water year 2008, and decreases to 20.9

mcm (16,900 af) for below normal water year 2010 and 18.7 mcm (15,200 af) for wet year 2006.

Critically dry year 2008 has environmental shortages of 6.8 mcm (5500 af) during weeks 1

through 5, 1.1 mcm (890 af) during weeks 27 and 28, and 23.0 mcm (18,600 af) in weeks 35

through 52. Similar results were found for below normal water year 2010. Fall shortages during

weeks 1 through 5 were 6.9 mcm (5600 af), with shortages beginning later in spring starting with

33

week 42 for a spring shortage volume of 14.0 mcm (11,300 af). Wet water year 2006 showed the

same period (weeks 1-5) and volume (6.8 mcm) of water shortage in the fall as 2008. However,

late spring shortages begin 8 weeks later starting in week 43 in late July with a shortage volume

of 11.9 mcm (9,600 af).

The option of purchasing the largest water rights holder in the system, LMMWC, gave the largest

decrease in annual environmental flow volume shortage for critically dry water year 2008 with a

decrease of 86% from baseline from 30.9 mcm to 4.3 mcm (Figure 16). The four wells

decreased environmental shortages by 28% and the combination of the four wells and the water

exchange agreement had a 24% environmental shortage reduction. The Droz and Orange Cove

water rights purchases had the smallest shortage decrease of 10%. The water exchange

agreement alone increases environmental flow shortages in the spring and summer months

when TNC water rights are made available for irrigation, which increase annual environmental

shortage for minimum instream flows by 3 percent. The results for the below normal and wet

water years show the same order, with LMMWC as the only option that gets close to eliminating

minimum instream flow shortages (Table 3).

34

Figure 15. Minimum instream flow shortages for critically dry (2008), below normal (2010), and wet (2006)

water years for baseline, 4 wells, water exchange agreement, agreement and 4 wells, Droz and Orange

Cove left instream, and LMMWC water left instream. The x-axis corresponds to water year weeks and the

y-axis corresponds to water volume shortages in mcm.

35

Figure 16. Percent change of minimum instream flow shortages for different water management

alternatives compared to baseline for critically dry water year 2008.

Sustainability Boundary Approach Case

Figure 17 shows modeled shortages for an 80 percent sustainability boundary approach

environmental target case. For critically dry water year 2008, weeks 1 through 5 have a shortage

of 6.7 mcm (5400 af) and weeks 27 through 52 have a shortage of 43.2 mcm (35,000 af) for a

total annual shortage of 49.9 mcm (40,000 af). Below normal water year 2010 experiences

shortages during the same weeks with a smaller volume, 6.4 mcm (5200 af) for the fall and 41.9

mcm (34,000 af) for the spring and summer for a total annual shortage of 48.3 mcm (39,000 af).

Wet water year 2006 has shortages during the same weeks 1 through 5 of 7.2 mcm (5800 af)

with spring shortages starting in week 30 through 52 of 35.1 mcm (28,000 af) for an annual

shortage of about 42.4 mcm (34,000 af).

36

Figure 17. SBA environmental shortages for critically dry (2008), below normal (2010), and wet (2006)

water years for baseline, 4 wells, agreement, agreement and 4 wells, Droz and Orange Cove purchase,

and LMMWC purchase management options. The x-axis is in water year weeks and the y-axis is water

volume shortages in mcm.

37

Effects of the different water management options to the SBA environmental flow case were

similar to the MIF case with little variation between water year types. For critically dry water year

2008, the LMMWC water right purchase decreases environmental water shortage by 97% of

base shortages, followed by a 21% decrease in environmental water shortages with the use of

four conjunctive use wells, a 19% decrease with the four well and water exchange agreement

combination, and an 8% decrease with the purchase of two water rights Droz and Orange Cove

(Table 3). The exchange agreement alone increases environmental shortage by 2% of baseline.

Figure 18. Percent change of 80% sustainability boundary approach flow shortages for different water

management alternatives compared to baseline for critically dry water year 2008.

38

Table 3. Annual volume of shortages for fish passage, MIF, and SBA environmental flow cases by water

year type and water management alternatives. Percent decrease in environmental flow shortage from

baseline indicated in parentheses.

Annual Volume of Environmental Flow Shortage (mcm)

Fish Passage mcm (% decrease)

2.55 cms MIF mcm (% decrease)

80% SBA mcm (% decrease)

WY 2008 Critically DryBaseline 3.0 30.9 49.94 Wells 1.2 (61%) 22.3 (28%) 39.3 (21%)Agreement 1.8 (41%) 31.9 (+3%) 39.3 (+2%)4 Wells & Agreement 0.2 (94%) 23.3 (24%) 40.4 (19%)Droz & Orange Cove 2.1 (31%) 27.8 (10%) 45.9 (8%)LMMWC - 4.3 (86%) 1.7 (97%)

WY 2010 Below NormalBaseline 2.1 20.9 48.34 Wells 1.0 (50%) 15.4 (26%) 37.7 (22%)Agreement 0.8 (60%) 22.1 (6%) 50.2 (+4%)4 Wells & Agreement 0.0 (100%) 16.7 (20%) 39.6 (18%)Droz & Orange Cove 1.7 (16%) 18.9 (9%) 43.9 (9%)LMMWC - 1.8 (92%) 1.1 (98%)

WY 2006 WetBaseline 2.0 18.7 42.44 Wells 1.0 (52%) 13.5 (28%) 33.4 (21%)Agreement 0.7 (62%) 20.6 (11%) 45.0 (+6%)4 Wells & Agreement 0.0 (100%) 15.2 (19%) 36.0 (15%)Droz & Orange Cove 1.6 (18%) 16.6 (11%) 38.5 (9%)LMMWC - 0.2 (99%) 0.7 (98%)

39

Discussion

This study has found that late October is a critical period of water scarcity in the lower Mill Creek

watershed, in which there is insufficient natural flow to meet all agricultural irrigation demands

and environmental fish passage requirements. This finding persists in all SVI water year types

from critically dry to wet. The fall fish passage shortages for all water year types is ranges from a

volume of 1.7 to 2.1 mcm (1400-1700 af). In contrast, the spring base flow requirements for fish

passage experience shortage during the critically dry water year, but not for the below normal

and wet water years. Since fall shortages occur during the last few weeks of irrigation, a potential

solution water scarcity solution is to shift the irrigation period to begin earlier in the spring, though

this depends on the feasibility and utility of early irrigation in the region. Model results indicate

that a water exchange agreement coupled with 4 wells could decrease fish passage flow

shortages by 94-100% (Table 3) with no curtailment to irrigation water supplies.

This information can help managers develop and select water management options that need to

for each water year condition. However, the frequency of water year types is unlikely to be static

with climate change (Null and Viers 2013), so it will be necessary for water management policies

to adapt to new conditions. Null and Viers found that the frequency of dry and critically dry years

is likely to increase, which would increase scarcity and increase the likelihood of not meeting

environmental flow targets. As target taxa are considered special status species, increased

regulatory action to limit further jeopardy may result. Further, changing hydroclimatic conditions

indicate more precipitation as rain, as opposed to snow, which will increase winter magnitudes,

40

limit snowmelt runoff, and increase low flow duration. This is likely to exacerbate environmental

flow shortages during late summer, a period with consistent unmet environmental demands.

Both the MIF and SBA environmental flow cases show that the only water management

alternative able to decrease the environmental flow shortages by more than 80 percent of

baseline is the purchase of the Los Molinos Mutual Water Company water rights, which are 68

percent of all total water rights in the system. Given the current water allocations in the system,

substantial curtailment of irrigation may needed to meet these environmental flow objectives.

This study developed and used a decision-support tool to quantify water scarcity periods through

use of a linear programming model in an Excel spreadsheet. While model results have identified

critical water scarcity periods and the effects of potential water management options in the Mill

Creek case study, some limitations are important to keep in mind. For example, water quality

parameters such as temperature are critical in supporting freshwater fish. In particular, the

survival of migrating fish depends on having not only sufficient water quantity to traverse riffles

but also water with temperature ranges appropriate for their physiology. While sufficient instream

flows affect stream temperature, this work focused primarily on water volume, and it is

recommended that future work address the potential effect of water transfers on water quality

parameters appropriate for freshwater fish species. In addition, future work that couples the loss

in agricultural revenue from water transfers can provide valuable insight on the economic costs of

meeting environmental flow requirements in diversion-impacted rivers. Finally, due to the scope

41

of this project, groundwater and surface water interactions could not be thoroughly investigated

and were not represented in the model. However, due to the alluvial nature of the valley reaches

of lower Mill Creek, it is likely that groundwater surface water interactions are present in the

system and future research should strive to address this issue.

Conclusion

This worked has demonstrated the development and use of a linear programming model to

explore the effects of different water management options to meet instream environmental flow

targets. Through its application to a case study on Mill Creek, late October and early November

are a critical period of water scarcity for fish passage during all water year types. This fall

passage period environmental shortage of 1.7 to 2.1 mcm (1400 – 1700 af) can be reduced

through water exchanges, wells, or shifting of the irrigation season. The output of the

decision-support tool can help inform when water transfer agreements should be negotiated to

meet fish passage flow requirements. Furthermore, this work can be extended to include a

broader range of riparian species or ecosystem processes as well as the adoption of novel water

resource infrastructure or irrigation methods. The model developed can be modified and applied

to other river systems with flow regimes impaired by water abstractions, such as other

watersheds in the Mount Lassen foothills such as Deer Creek as well as coastal rivers in

Northern California subject to flow regime impairment through small diversions.

42

References

Acreman, M., A. H. Arthington, M. J. Collof, C. Couch, N. D. Crossman, F. Dyer, I. C. Overton, C.

A. Pollino, M. J. Stewardson and W. Young (2014). "Environmental flows for natural, hybrid, and

novel riverine ecosystems in a changing world." Frontiers in Ecology and the Environment 12(8):

466-473.

Acreman, M., M. Dunbar, J. Hannaford, O. Mountford, P. Wood, N. Holmes, I. Cowx, R. Noble, C.

Extence, J. Aldrick, J. King, A. Black and D. Crookall (2008). "Developing environmental

standards for abstractions from UK rivers to implement the EU Water Framework Directive."

Hydrologic Sciences Journal 53(6): 1105-1120.

Arthington, A. H. (2012). Environmental Flows: Saving Rivers in the Third Millennium. Berkeley

and Los Angeles, CA, University of California Press.

Baron, J. S., N. L. Poff, P. L. Angermeier, C. N. Dahm, P. H. Gleick, N. G. Hairston, R. B.

Jackson, C. A. Johnston, B. D. Richter and A. D. Steinman (2002). "Meeting ecological and

societal needs for freshwater." Ecological Applications 12(5): 1247-1260.

Brisbane Declaration (2007). The Brisbane Declaration: environmental flows are essential for

freshwater ecosystem health and human well-being. . Declaration of the 10th International River

Symposium and International Environmental Flows Conference. Brisbane, Australia.

43

Bunn, S. E. and A. H. Arthington (2002). "Basic Principles and Ecological Consequences of

Altered Flow Regimes for Aquatic Biodiversity." Environmental Management 30(4): 492-507.

CA Department of Fish and Wildlife (2015). State and Federally Listed Endangered and

Threatened Animals of California. C. D. o. F. a. Wildlife.

CA State Water Resources Control Board (2015). Curtailment Order in the Matter of Diversion of

Water from Antelope Creek Tributary to the Sacramento River in Tehama County. WR

2015-0017-DWR. Sacramento, CA.

Cederholm, C. J., M. D. Kunze, T. Murota and A. Sibatani (1999). "Pacific Salmon Carcasses:

Essential Contributions of Nutrients and Energy for Aquatic and Terrestrial Ecosystems."

Fisheries 24(10): 6-15.

Deitch, M. J., M. A.M. and S. Feirer (2013). "Cumulative Effects of Small Reservoirs on

Streamflow in Northern Coastal California Catchments." Water Resources Management 27:

5101-5118.

Dudgeon, D. (2010). "Prospects for sustaining freshwater biodiversity in the 21st century: linking

ecosystem structure and function." Current Opinion in Environmental Sustainability 2(5-6):

422-430.

44

Dudgeon, D., A. H. Arthington, M. O. Gessner, Z. Kawabata, D. J. Knowler, C. Leveque, R. J.

Naiman, A. H. Prieur-Richard, D. Soto, M. L. Stiassny and C. A. Sullivan (2006). "Freshwater

biodiversity: importance, threats, status and conservation challenges." Biol Rev Camb Philos Soc

81(2): 163-182.

Dunning, H. C. (1989). "The Public Trust: A Fundamental Doctrine of American Property Law."

Environmental Law 19: 515-525.

DWR, C. (2013, 12/19/13). "Chronological Reconstructed Sacramento and San Joaquin Valley

Water Year Hydrologic Classification Indices." Retrieved 9/12/14, 2014, from

http://cdec.water.ca.gov/cgi-progs/iodir/WSIHIST.

Gende, S. M., R. T. Edwards, M. F. Willson and M. S. Wipfli (2002). "Pacific Salmon in Aquatic

and Terrestrial Ecosystems." BioScience 52(10): 917.

Heiman, D. and M. L. Knecht (2010). A Roadmap to Watershed Management, Sacramento River

Watershed Program.

Howard, T. (2014). National Marine Fisheries Service and California Department of Fish and

Game Voluntary Drought Agreements on Mill Creek. C. S. W. R. C. Board. Sacramento, CA.

Jager, H. I. (2014). "Thinking outside the channel: Timing pulse flows to benefit salmon via

indirect pathways." Ecological Modelling 273: 117-127.

45

Kiernan, J. D., P. Moyle and P. K. Crain (2012). "Restoring native fish assemblages to a

regulated California stream using the natural flow regime concept." Ecological Applications 22(5):

1472-1482.

Koehler, C. L. (1995). "Water Rights and the Public Trust Doctrine: Resolution of the Mono Lake

Controversy." Ecology Law Quarterly 22(3).

Moriasi, D. N., J. G. Arnold, M. W. Van Liew, R. L. Bingner, R. D. Harmel and T. L. Veith (2007).

"Model Evaluation Guidelines for Systematic Quantification of Accuracy in Watershed

Simulations." Transactions of the ASABE 50(3).

Moyle, P. (2002). Inland Fishes of California, University of California Press.

Naiman, R. J. and D. Dudgeon (2011). "Global alteration of freshwaters: influences on human

and environmental well-being." Ecological Research 26(5): 865-873.

Null, S. E. and J. H. Viers (2013). "In bad waters: Water year classification in nonstationary

climates." Water Resources Research 49(2): 1137-1148.

Palmer, T. (2012). Field Guide to California Rivers. Berkeley and Los Angeles, California,

University of California Press.

46

Poff, N. L., J. D. Allan, M. B. Bain, J. R. Karr, K. L. Prestegaard, B. D. Richter, R. E. Sparks and

J. C. Stromberg (1997). "The natural flow regime." Bioscience 47(11): 769-784.

Postel, S. L. and B. D. Richter (2003). Rivers for Life: Managing Water for People and Nature.

Washington, D.C., Island Press.

Richter, B. D., J. V. Baumgartner, J. Powell and D. P. Braun (1996). "A method for assessing

hydrologic alteration within ecosystems." Conservation Biology 10(4): 1163-1174.

Richter, B. D. and G. A. Thomas (2007). "Restoring Environmental Flows by Modifying Dam

Operations." Ecology and Society 12(1).

Rood, S. B., G. M. Samuelson, J. H. Braatne, C. R. Gourley, F. M. R. Hughes and J. M. Mahoney

(2005). "Managing river flows to restore floodplain forests." Frontiers in Ecology and the

Environment 3(4): 193-201.

Sala, O. E., F. S. Chapin III, J. J. Armesto, E. Berlow, J. Bloomfield, R. Dirzo, E. Huber-Sanwald,

L. F. Huenneke, R. B. Jackson, A. Kinzig, R. Leemans, D. M. Lodge, H. A. Mooney, M. n.

Oesterheld, N. L. Poff, M. T. Sykes, B. H. Walker, M. Walker and D. H. Wall (2000). "Global

Biodiversity Scenarios for the Year 2100." Science 287(5459): 1770-1774.

47

Shiau, J.-T. and F.-C. Wu (2013). "Optimizing environmental flows for multiple reaches affected

by a multipurpose reservoir system in Taiwan: Restoring natural flow regimes at multiple

temporal scales." Water Resources Research 49(1): 565-584.

Shiklomanov, I. A. (1993). World fresh water resources. Water in Crisis: A Guide to the World's

Fresh Water Resources. P. H. Gleick. New York, Oxford University Press: 13.

Superior Court of Tehama County (1920). Los Molinos Land Company & Coneland Water

Company vs Clarence V. Clough. S. C. o. T. County.

Swain, D. L., M. Tsiang, M. Haugen, D. Singh, A. Charland, B. Rajaratnam and N. S. Diffenbaugh

(2014). "The extraordinary California drought of 2013/2014: Character, context, and the role of

climate change." Bulletin of the American Meteorological Society 95(9): S3-S7.

Tharme, R. E. (2003). "A global perspective on environmental flow assessment: emerging trends

in the development and application of environmental flow methodologies for rivers." River

Research and Applications 19(5-6): 397-441.

Vorosmarty, C. J., P. B. McIntyre, M. O. Gessner, D. Dudgeon, A. Prusevich, P. Green, S.

Glidden, S. E. Bunn, C. A. Sullivan, C. R. Liermann and P. M. Davies (2010). "Global threats to

human water security and river biodiversity." Nature 467: 555-561.

48

Yarnell, S. M., J. H. Viers and J. F. Mount (2010). "Ecology and Management of the Spring

Snowmelt Recession." Bioscience 60(2): 114-127.

Yin, X., Z. Yang and G. Petts (2011). "Reservoir operating rules to sustain environmental flows in

regulated rivers." Water Resources Research 47.