Modeling Water Rights

Introduction
Water law often drives the decisions made in operations and planning of water systems. Water law is the foundation for administering and managing water supplies. Because of the importance of water law in water planning and operations modeling, water rights modeling capability in your model should adequately represent the legal systems currently in place.

This post summarizes the basic legal systems used to manage and facilitate allocation of limited water supplies. The summaries of legal systems presented in this post are founded on my understanding of U.S. Water Law and a cursory review and comparison of systems used in Canada and Australia. Following a short description of each basic legal system, a summary of modeling requirements for the system is explored.

Legal Systems for Water Allocation
For the purposes of this post, I refer to a water user as an “account.” All accounts have a demand for water and a water right that justifies use of their water. Water rights are used to manage and administer allocation of limited water supplies. Types of water rights include:

•  The right to divert water from a stream (i.e. to a WTP, reservoir, canal, etc.)
•  The right to store water in a reservoir or groundwater aquifer
•  The right to use flow thru demand (i.e. instream fish flows, mills, recreation, etc.)
•  The right to pump water from groundwater
•  The right to capture diffused water

Water rights are administered using one (or combination of) of a multitude of basic legal doctrines. The most fundamental doctrines of water law include:

•  Riparian Right
•  Prior Appropriation
•  Absolute Ownership
•  Reasonable Use

Riparian Rights

Riparians are landowners who own property that borders a waterway. Under the riparian doctrine, all riparians have the right to make reasonable use of the water that borders their land. Some riparian rights allow for multiple uses so long as the quantity and quality is preserved. Riparian water rights work well for flow thru uses such as supplying water to saw mills, navigation, fishing, and recreation. Modern riparian rights allow for consumption of flows for domestic use cases. Riparian water law generally applies to states east of the Mississippi River (Currently used in 29 of the U.S. states).

Allocation of Limited Water Supply
If there is not enough water to satisfy all users, allotments are generally fixed in proportion to frontage on the water source or the size of the riparan parcel. These rights cannot be sold or transferred other than with the adjoining land, and water cannot be transferred out of the watershed. If water is naturally available, then you can take water on an “as-need” basis up to your allotment specified in a permit.

Requirements for Model Implementation
Water must be distributed in proportion to properties of the account, such as property size or riparian frontage length. Shortages are shared among all users with possible exceptions. The exceptions would be treated as higher priority of other uses, and therefore would trump others. The effects of an upstream allocation on a downstream riparian right must take into account lags and losses as water moves downstream.

Prior Appropriation
Prior Appropriation doctrine applies to the United States west of the Mississippi River and in areas where water is scarce. In contrast to the Riparian water rights system, prior appropriation doctrine specifies that rights depend on water use and not land ownership. Once beneficial use of the water can be established (perfecting the right), the right becomes permanent, so long as the right is not abandoned. The water right of a user with an older date of first use has priority over a newer water right. Higher priority water rights are known as “Senior” rights while lower priority rights are known as “Junior” rights. Appropriation rights can be transferred because location of use relative to the water source is not considered as criteria for the right.

Allocation of Limited Supply
When the amount of natural flow in the river is not sufficient to satisfy all water needs, water supply must first satisfy senior water rights before allocation to more junior rights are made.

Requirements for Model Implementation

•  Senior water rights must be satisfied before junior water rights.
•  Equal priorities are curtailed relative to their flow needs
•  The user must be able to define custom boundary conditions for the water use permit (i.e. timing, max flow rate, accrual based maxima, etc.)
•  Sometimes, diversion of water to service a demand is limited by physical constraints of the hydraulic system rather than the water right
•  The effects of an upstream allocation on a downstream senior right must take into account lags and losses as water moves downstream.
•  Releases from reservoir storage accounts are not priority date driven and are therefore not included in the prior appropriation allocation process. Diversions to reservoir storage accounts are treated like any other stream diversion right

Hybrid Systems
Hybrid systems are used for areas that started out with a riparian right scheme then later converted to prior appropriation law, while maintaining the existing riparian rights in place. Your model may need to be capable of simulating hybrid systems.

Special Types of Water
Most water available for use falls within one of the three legal systems stated above, but special types of water fall outside of those systems. These are Groundwater and Diffused Surface Water.

Groundwater

Groundwater right law is tricky because it is most in flux within modern legal systems. Until recently, groundwater was loosely considered to be a non-depletable resource and the effects of our usage were unknown. For a long time, groundwater was simply not managed or allocated. Today, many laws have been established to treat groundwater as part of the surface water system and/or with rules that are different from rules used for allocation of surface waters. Groundwater withdrawals in the Sacramento Valley of California are still not managed.

Groundwater is treated differently because users are able to extract water from the source at a faster rate than what replenishes the source. Another unique problem is that a new diversion (well) might endanger existing accounts in the same aquifer.

Allocating Limited Supplies of Groundwater
Absolute Ownership
A landowner has an unlimited right to withdraw any water found beneath the owned land. The account with the biggest pump and deepest well gets the most water.

Your model needs to be able to allocate water flows based on the properties of the account, like pump size and well depth. The total, available water supply is limited to the amount available in the aquifer.

Rights of Prior Appropriation
The person who started pumping (using) the water first has the highest priority to use the water. This is not very practical because absolute protection of the user’s right is not possible. This system is used mainly for groundwater that is connected hydraulically to surface water bodies. Sometimes the total withdrawal rates are set in accordance to what the total recharge rate is.This system can be implemented in your model the same way surface waters are allocated.

Groundwater as a Public Resource
Most jurisdictions recognize groundwater as public property. In areas where groundwater is not considered to be public property, appropriations are governed by doctrines of “reasonable use”, “correlative rights”, and other bases. Application of reasonable use doctrine means that your model must be able to model accounts with priorities. Priorities can be defined using properties that represent some measure of reasonable use. Application of correlative rights means that shortages need to be shared across all accounts.

Diffused Surface Water
Not all water types are able to be managed by governments. Thus, water right legal systems exclude from coverage oceans, water in the process of evaporation or transpiration, and precipitation. Most jurisdictions allow landowners to make use of diffused surface water on their property without limitation. In these cases, we would assume the doctrine of absolute ownership of the diffused water.

Precipitation and evaporated water can only be captured within the property the water accumulates in. Because of this, there is no need to allocate the water. Ocean water use (i.e. desalination) likely will be modeled as an infinite source so allocation is not needed.

Conclusions
It appears that all the doctrines of water law can be simulated using one (or a combination) of two methods:

•  Shared appropriation
•  Priority appropriation

The challenges we are faced with in designing a model to be used for water rights are:

•  Water is owned property that is constantly changing through time and space
•  The study of water law is a relatively young and dynamic field
•  There are many different ways to administer and manage water use depending on the location, nature of the water system, and the history of the legal systems currently in use

Another challenge in modeling water rights is the simulation of “colored water”. This is where water that belongs to an account is separated from water belonging to other accounts. I have not seen an existing tool that handles this very well. I’m not sure yet if it would be worth our time to implement this ability.

References
Getches, David H. "Water Law in a nut shell". 1984.
Sax, Joseph L., et al. "Legal Control of Water Resources, Cases and Materials." Third Edition, 2000.
Nowlan, Linda. "Customary Water Laws and Practices in Canada", 2010.
Australian Office of Legislative Drafting and Publishing. "Water Act 2007", Attorney General's Department, Canberra. 2011