1. CE 3372 Water Systems Design Lecture 003 – Design Criteria and Demand Estimation

2. Outline Design criteria – Examples Estimating System Demand (or Capacity) – Water supply demand; population basis

3. Design Criteria Negotiable and non-negotiable constraints Negotiable constraints – Pipeline alignments – Pipeline depths – Channel geometry

4. Design Criteria Negotiable and non-negotiable constraints Non-Negotiable constraints – Continuity, Momentum, Energy Water flows downhill, unless power and money are applied Semi-Negotiable – Rules takes a long time to change takes a lot of money for a variance

5. Design Criteria Non-negotiable constraints are dictated by laws of physics, chemistry (and to some extent mankind) Negotiable constraints are the design variables that can be adjusted to satisfy the non-negotiable constraints.

6. Design Criteria Design manuals Codes, Guidance Documents, etc. – These contain many “non-negotiable” constraints, and in essence guide a large part of design. – Consider the TAC with regards to drinking water supply : the minimum spacing of a water line and a sewer line is a “non-negotiable” constraint. the pipe size, once above the minimum is negotiable.

7. Design Manuals Where do we get the guidance documents? – Texas Administrative Code

8. Design Manuals Where do we get the guidance documents? – Texas Administrative Code Part 1, Chapters 30 and 31 cover nearly all of what we might do as municipal water engineers Large diameter pipelines like the Lake Allen Henry to Lubbock are outside the scope of the code and are governed by broader guidance – these kinds of projects are uncommon and likely closely follow the intent of the TAC as appropriate.

9. Design Manuals Where do we get the guidance documents? – Flood Control Districts

10. Design Manuals Where do we get the guidance documents? – Local Jurisdictions

11. Design Manuals Where do we get the guidance documents? – Professional Organizations Not everything is free – this MOP would be vital to a practicing engineer, but he/she would have to pay for it

12. Design Manuals Where do we get the guidance documents? – Professional Publications – Often these publications are eventually integrated into jurisdictional design manuals. – The example shown is the source of minimum sewer velocity criteria in the USA

13. Design Manuals Where do we get the guidance documents? – Vendor/Trade Organization Publications

14. Design Protocol Most design projects are defined by – Geographic location Nation, State, County – possibly a city. Get appropriate jurisdictional codes, criteria, etc. that are available. – Client (who pays) Might be able to help – esp. if the client is also a jurisdictional entity. – Activities Things that have to get done, includes materials and construction.

15. Design Protocol Once you define the location – Obtain the relevant manuals, in Texas usually the TAC, a county manual, and city ordinances will apply. – For missing items, use professional manuals of practice (there is liability protection for using a MOP – they represent current state-of-practice) – For obscure items, use professional publications

16. Protocol As you define the activities – Obtain the relevant vendor materials manuals and guidance documents – Cross-check suggested application with the jurisdictional codes (and MOPs) – Obtain variances if you think a better solution exists, but requires a non-certified material or construction process.

17. Demand/Use Agriculture – 50% of water is consumptive use. Seasonal and may be inversely related to natural water availability Navigation Hydroelectric Power/Steam Electric Generation Manufacturing – Process Waters – Cooling Waters

18. Demand/Use Natural Systems – Instream flow requirements – Lake levels – Protection of fish and wildlife Cities and Other Communities – Drinking, cooking, laundry, pooping – Street cleaning – Fire demand – Landscaping – Commercial Use Recreation

19. Demand How much water is going to be required? – Regional Level Estimate population growth Estimate water requirements for population – Subdivision Level Estimate water requirements for planned development

20. Demand/Use WWI – American Forces Water Allocations – Army advancing: 0.5 gpd/soldier. – Army static: 1.0 gpd/soldier. – Field Hospital: 5.5 gpd/soldier. – Rear Areas: 10.0 gdp/soldier. – Base Hospital: 25.0 gpd/soldier. From: The Story of Man’s Quest for Water. Jasper Owen Draffin. The Garrard Press. 1939.

21. Demand Estimation Water demands on a system need to be estimated in advance of design or retrofit. Demand depends on the type of customer: – Residential demand: water used in homes and apartments. Usually estimated by volume/day/person. Usually quite variable, with peak to average ratios approaching 4. – Commercial demand: water used in motels, restaurants, air conditioning, and similar activities. More predictable than residential.

22. Demand Estimation Water demands on a system need to be estimated in advance of design or retrofit. Demand depends on the type of customer: – Industrial demand: water used in industry, manufacture, and similar activities. Includes “product” water; water bound in the product such as soft-drinks and such. Sometimes supplied separate from municipal system, but not always. Principles of design are the same. – Agricultural demand — water used in agriculture. Large volumes, not usually part of a municipal system.

23. Average Demand Average demand is estimated based on the types of customers and the demand locations. Generally tabulated by various organizations – AWWA, ASCE and WEF would be good starting places. – For regional scale estimation, USGS Circular 1200 (in Readings). – For commercial buildings and structures of that nature, an alternative based on the fixture type and fixture count (.i.e. toilets, sinks, restaurant sinks.).

24. Average Demand Regional Estimation – The amount of water used in a locality is directly related to the size of the population. – Errors in projecting population changes affect water use projections as well. Engineers normally do not conduct these analyses, as this is in the realm of social scientists and economists. As an example, many smaller suburban communities actively recruit different types of industries that could have vastly different water demands and impacts on the local population.

25. Average Demand Population Models (Quick Background) – Two Growth Models Typically Used Arithmetic – project future using a constant slope line. Exponential – project future using exponential curve. – Check past census data to see which is more appropriate

26. Average Demand Population Models (Quick Background) – Declining growth model. – Curvilinear method. – Area/Ratio method (based on census ratios)

27. Average Demand USGS Circular 1200

28. Average Demand Subdivision Scale – Average flow distribution. What is the median average flow from this information?

29. Peak Demand Peak demand ranges from 1.5 to as much as 5 times average daily use, excluding fire flow. Usually the maximum daily consumption plus fire flow is larger than the maximum hourly demand, but not always. – In the case where the peak hourly exceeds the maximum daily plus fire flow the peak value should be used for design.

30. Peak Demand Peak flow ratio adjustments by population and reference flow

31. Peak Demand Peak flow ratio adjustments by operational conditions

32. Pressure Requirements Pressure requirements in the system depend on the combined normal service requirements and fire flow demand. – Pressures must be high enough (at the pump) to overcome energy losses within the system. – Additionally pressure requirements are a function of the topography. – Water distribution systems are usually installed at minimum depth (very close to grade) so that the pipes closely follow the topographic relief of the area.

33. Pressure Requirements System pressures are adapted to such requirements. – In hilly areas booster pumping may be required. – Exact minimum pressures in a system vary from state to state, and the minimums are usually established by the state’s Health Department or similar agencies. – The state Fire Marshall may establish additional requirements.

34. Pressure Requirements Typically 20 psi is an absolute minimum pressure in a distribution system when providing the maximum daily demand including fire flow or the peak hourly demand. – The minimum pressure is a safety requirement to prevent potential back flows from house fixtures, and still have enough energy to push water up three stories.

35. Pressure Requirements Desirable pressure ranges are 40-60 psi in a residential area, with a typical upper limit of about 80 psi. – Above 80 psi, household fixtures are easily damaged and pressure reducing valves are required. – In commercial areas, a nominal pressure of 75 psi is desirable (commercial fixtures are built more ruggedly than residential).

36. Fire Flow Requirements Each jurisdiction establishes its own fire flow requirements. – As a guideline the ISO (Insurance Services Office) has several approaches for fire flow estimation. – Single structure: – Population based:

37. Assigning Demand The network models usually built at large scale (city-size) contain nodes that represent a multitude of actual connections. – While conceptually possible to model to every single connection, to date this practice is discouraged, because the model is hard to maintain small errors during development go unnoticed the operation of any single connection is not well known.

38. Assigning Demand Typically a skeleton model is used where individual demands are grouped and assigned to an appropriate node. Cleveland, T.G., Rogers, J. R., Chuang L., Yuan, D, Reddy, B. and Owens, T. 1996. Research into Production Cost Reduction by Energy Management of Houston's Surface and Groundwater System. Final Report to Planning and Operations Support, Department of Public Works and Engineering, City of Houston, Houston, TX, 178p

39. Assigning Demand Determine skeleton (pipe sizes to consider)

40. Assigning Demand Build Network Model, Nodes and Links

41. Assigning Demand Overlay Locations onto Network Simulator Address Matching (from Billing Records) => Generate Demand Locations

42. Assigning Demand Nearest L-2 Neighbor Algorithm => Associate Address (and Demand) to a Node

43. Assigning Demand Demand Pattern (Each Node corresponds to particular customers)

44. Assigning Demand Now add Supply Locations => Simulate “What-If?”

45. Assigning Demand The challenge is in how to skeletonize – Analysis (as in Houston study), focus on enough detail for the “what-if”. – Design focus on detail for “what-if” as well as topology of the network.

46. Assigning Demand Distribution systems – Gravity uncommon: Ancient Rome, New York (circa 1800s) – Pumped with marginal storage. Houston (circa 1990s) – Pumped with substantial (several hours) of storage. Most other systems in USA.

47. Gravity System Dependable – Source of supply must be located well above the city – High-pressure demand for fire-fighting may require pumper trucks

48. Pumped (Marginal Storage) Least Desirable – Pressures vary substantially with variations in flow – Provides no reserve if power failure

49. Pumped with Storage Most common Water supplied at approximately uniform rate Flow in excess of consumption stored in elevated tanks Tank water provides flow and pressure when use is high – Fire-fighting – High-use hours – Flow during power failure Storage volume throughout system and for individual service areas typically 15 –30% of maximum daily rate.

50. Network Types Branch – No circulation – Has terminals and dead-ends. Water in dead-ends is stagnant Disinfection residual Corrosion

51. Network Types Grid/Loop – Furnishes supply from more than one direction Water circulates – Disinfection is more effective. – Water “age” in system is younger (fresher). In case of water main break, fewer people are inconvenienced

52. Network Types Loop vs. Branch during network failure. – Every link in a branch system is a single point of failure that isolates all downstream nodes. – No so with loop, only main supply line is such.

53. Pipe System Primary Mains (Arterial Mains) – Form the basic structure of the system and carry flow from the pumping station to elevated storage tanks and from elevated storage tanks to the various districts of the city Laid out in interlocking loops Mains not more than 1 km (3000 ft) apart – Valved at intervals of not more than 1.5 km (1 mile) – Smaller lines connecting to them are valved

54. Pipe System Secondary Lines – Form smaller loops within the primary main system – Run from one primary line to another Spacings of 2 to 4 blocks – Provide large amounts of water for fire fighting with out excessive pressure loss

55. Pipe System Small distribution lines – Form a grid over the entire service area – Supply water to every user and fire hydrants – Connected to primary, secondary, or other small mains at both ends Valved so the system can be shut down for repairs Size may be dictated by fire flow except in residential areas with very large lots

56. Collection Systems Capacity (demand) estimation is for later in the course. – Involves hydrology (usually) – Capacity is usually dependent on area served (in contrast to population served) Wastewater demand can be reasonably estimated as some fraction of the freshwater demand.