A National Diversion Database Slide 1 (Intro slide) This presentation will focus on how water diversions are portrayed in the National Hydrography Dataset – the NHD, and the Watershed Boundary Dataset – the WBD. We will find that the NHD and WBD are an excellent framework around which to encode the nation’s water diversions
Slide 2 First of all, what is a diversion? A diversion is the non-natural engineered transfer of water. It is designed to remove water from the natural flow network and reintroduce it back into the natural flow network at a different location, or to consume that water. Typically this transfer is conveyed through a ditch, canal, aqueduct, pipeline, gate, culvert, siphon, penstock, or flume. A diversion may also employ a natural stream for part of its movement and often involves storage in a reservoir or lake.
Slide 3 Diversions revolve around four key elements. The first is the point of removal. This is the location on the network where water is withdrawn from the natural network. Second is the conveyance. This is the engineered system that transfers the water. Third is the point of addition, where water is reintroduced to the natural network. Fourth is water use, the point on the network where water is consumed, effectively removing it from the water balance equation.
Slide 4 The NHD is a highly detailed representation of the nation’s surface water, containing all the surface water features found on a topographic map. It is composed of 7.5-million miles of rivers and streams, and contains over 6.5-million lakes and ponds. This data is modeled into a flow network enabling downstream or upstream navigation.
Slide 4 – click Within this geospatial data we can represent diversions. In this case a 23 mile long diversion tunnel that withdraws 300 cubic feet per second from the natural network.
Slide 5 As a companion dataset to the NHD, the WBD represents drainage basins.
Slide 5 – click With this we can also represent the natural flow of water.
Slide 5 – click And also represent the flow of diverted water.
Slide 6 Let’s look at some examples of the basic infrastructure for water diversions. Things like dams, gates, pipelines, aqueducts, reservoirs, and water use facilities. All of these are, or can, be represented in the NHD. This gives us the basic elements on which to model diversions.
Slide 7 Water diversions can be roughly classified as two types. One is what we call long-distance transfers. These are typically basin-to-basin transfers and usually involve aqueducts and pipelines inside of tunnels. This example of the Big Thompson project in Colorado involves reservoirs, tunnels, aqueducts, and natural streams to move water from the Pacific Watershed to the Atlantic Watershed.
Slide 8 The second type of diversion is what we call short-distance diversions. These are typically associated with water use. They move water from the natural or diverted system for fairly immediate consumption. Examples include water consumption in a thermoelectric powerplant or in agricultural irrigation.
Slide 9 Long distance, or basin-to-basin, diversions can occur at various levels of the drainage area hierarchy. The highest level is the hydrologic region transfer such as the Colorado River Aqueduct moving water from the Lower Colorado Region to the California Region. To do this, water must be pumped up and over the natural divide separating the two.
Slide 10 The next level is the hydrologic sub-regional transfers such as the California Aqueduct, which moves water within the California Region between multiple hydrologic sub-regions from the Central part of the state to the southern part of the state.
Slide 11 In fact, California is crisscrossed with many aqueducts moving water into and around the state. All of these are represented in the NHD.
Slide 12 The third level of diversions are between hydrologic sub-basins. This is the movement of water within sub-regions, but between sub-basins.
Slide 13 The fourth level of diversions is recorded at the hydrologic sub-watershed. This is getting pretty detailed. Why are we doing this?
Slide 14 Because the Water Census of the United States is concerned with the water budget model on a sub-watershed. There are many components to a water budget involving surface water, ground water, and the atmosphere. In many sub-watersheds diverted water is not an issue, but in many more it is a factor, and in many it is a key factor. Without an account of water diversions water budgets cannot be accurately calculated. The NHD and WBD are excellent platforms on which to inventory such water diversions.
Slide 15 Let’s take a close look at an Inter-Regional diversion. The brown side of the image represents the Pacific watershed while the green side represents the Atlantic watershed. The red dots represent locations where water is removed from the natural drainage network in the Pacific watershed and the green dots represent corresponding locations where water is added to the drainage network of the Atlantic watershed.
Slide 16 In this example water is removed from the collection reservoir of Lake Dillon in the Pacific watershed and by gravity flows down through a 23-mile tunnel to a portal where the water is added to the natural drainage of the North Fork of the South Platte River. The water ultimately supplies Denver with water. The reservoir, tunnel, and river, are all part of the NHD.
Slide 17 Let’s take a closer look at Lake Dillon in the Pacific watershed. Note that the Point of Removal is on the magenta colored lines representing the flow network in the lake. Meanwhile, the actual Gate where the water enters the tunnel is geographically located on the shore of the lake. In the NHD water is represented in a spatial context, and in a network context. The Point of Removal exists within the network context, while the Gate exists within the spatial context. The tunnel itself conveys the water in both the spatial and network context.
Slide 18 To illustrate this, here is the NHD in a spatial context with a point of removal.
Slide 19 Here is the same NHD in a network context with a point of removal.
Slide 20 Now let’s look at the corresponding Point of Addition for Lake Dillon. This takes place at the East Portal on the opposite end of the Roberts Tunnel in the Atlantic Watershed. Note that the geometry of the NHD doesn’t quite match what we see on the imagery. None-the-less we have a tie-in where the diversion reconnects with the natural network using the Point of Addition. Then a short distance away is the actual gate location.
Slide 21 Now let’s turn our attention to the Central Arizona Project, which like the Roberts Tunnel, also diverts Colorado River water.
Slide 22 A major aqueduct starts at Parker Dam on the Colorado River and delivers water throughout Arizona. Each of the blue dots is a point of water use.
Slide 23 Here again we see the Removal Point on the network, which is different than the actual spatial gate location. [Look at this slide for a moment]
Slide 24 Along the route of the Central Arizona Project aqueduct there are occasional en-route processes such as a pumping station to raise the elevation of the aqueduct so it can continue to flow by gravity.
Slide 25 Another en-route process is a siphon where the aqueduct flows under a Wash so that sediment from the Wash will not contaminate the aqueduct.
Slide 26 Then we come to the first point of water removal from the aqueduct. We call this a second order removal because it is a removal from a removal. Water is first diverted from the Colorado River and then again from the aqueduct using a lateral aqueduct.
Slide 27 The water travels a relatively short distance to a point of water use – irrigating agricultural lands. Since the water is not precisely used at a point, we call this non-point water use. None-the-less, in the NHD, a point will be designated on the network as a Point of Water Use.
Slide 28 Further down the aqueduct there is another Point of Water Use, this time at a water treatment plant in Phoenix. Here the water will be processed and redistributed in a secondary water use network which is not part of the NHD.
Slide 29 Another example is further down the aqueduct between Phoenix and Tucson at another agricultural complex.
Slide 30 Finally the water reaches Tucson 336 miles from the Colorado River and ultimately the water is pumped underground to recharge the aquifer.
Slide 31 We have seen how the NHD represents this major water diversion, but the WBD can also be used to represent it. The hydrologic sub-watersheds, or HUC12’s, can then be encoded as removing and adding water, and as consuming water.
Slide 32 Another example of a water diversion occurs along the Platte River in Nebraska. Here water is removed from the Platte River, flows through a parallel canal network to irrigate agricultural lands, and then has a Return Flow, where residual water is returned back to the natural network.
Slide 33 Another good example of Return Flow occurs at a thermoelectric powerplant. Thermoelectric powerplants account for 49% of water consumption in the United States. Of the water that is used, 10% is actually consumed and 90% is returned as a Return Flow. In the NHD network this is identified with a Removal point, and a corresponding Addition point indicating the Return Flow.
Slide 34 A few more examples to conclude the presentation. Here we see water routed through the San Diego Aqueduct to supply the storage reservoir - San Vicente Reservoir. Note that there is a point of Addition on the network to indicate the completion of the water transfer though the diversion. This will then signal to the water budget equation the addition of water through a diversion.
Slide 35 Here is another example where water is delivered to a storage reservoir through a diversion using a Point of Addition, effectively adding to the water budget of the HUC12. The water then continues its journey down a natural river. This will be a natural surface water loss to the water budget. However, before the water leaves the HUC12 in the river, yet another diversion will signal a Removal.
Slide 36 Just to point out that not all diversions are in the West, here is an example of the New York City water supply from the Catskill/Delaware and Croton Watersheds noting the use of diversion aqueducts.
Slide 37 We believe that the NHD and WBD, both completed national datasets, are fully capable of storing information on the nation’s water diversion systems and should be further developed to do this. To make it happen will require the stewards of the data to encode the necessary diversion information. On top of the work done by the stewards, the USGS will need to provide supplemental information and then ensure the overall quality of the data. This will provide an accurate mapping of the nation’s surface water network and provide key cross-checks to water budget equations to account for water gains and losses through diversions.