This subject tends to be complex, and normally design handled by licensed civil engineer and interface with hydrologist. Rainfall, runoff and flood data are reviewed, watershed conditions and sizing relative to each culvert or bridge crossing, addressing land uses, impervious surfaces, dam and pond storage, topography, soils, geology, etc. Sediment and channel type and instability can be factors to consider. In addition, aquatic life can be affected. Unless you have the credentials and license, you may be taking on legal or civil liabilities related to life, property, structural safety and integrity, or other resources. Most of this can be learned with diligence if you have the long term interest in civil engineering, hydrology, available data and literature search, etc. Models and equations to fit individual circumstances may be available, with assumptions, uncertainties, etc. often attached that should be considered. If you develop a plan or design, at least have it reviewed or certified by a licensed civil engineer.

Mr. Hansen;

Thanks for your answer and opinion. Not only I have all the skills and knowledge which you specify but also I have been adequate education about this. I'm just curious your vision, opinion, software recomendations and experience about this complex design. I hope you help me about these topics.

Thanks.

Hi Yazgan,

Here are a few ideas:

• First you need to be able to define performance metrics (or objectives) for your infrastructure. For example, usually you would want your system to be able to convey enough water for a given set of design storms (with T return period) without overflowing, and you want it to be affordable. Other aspects are also important, as William F. Hansen mentioned, such as structural safety, environmental impacts, maintenance requirements, code compliance, etc.
• Once you have a clear view on what your design criteria are, you will want to put them in a model that lets you try different alternatives so that you can assess if your design meets them. For example, I would use EPA-SWMM for defining the slope and dimensions (e.g., diameter) of conduits so that the design storms do not overflow the system. I think SWMM should be capable enough to be able to model the interactions between elements as culverts, catch basins, forced mains, tanks, spillways, etc.
• You can use a divide-and-conquer strategy for different aspects of your design: of course you would need structural software to determine the materials or compute the costs of your elements, and geotechnical models to verify your foundations. But you can also divide the hydraulic and hydrologic problem by, for example, computing your design flows in HEC-HMS, and then using the resulting hydrographs as an inputs in SWMM.
• If there are strong interactions between design decisions, like between the sizes of different elements, you might want to consider an optimization perspective, in which you try multiple combinations and see which one can meet the design criteria better or at the lowest cost. For example, pipe network design is done this way because changes in the diameter of one pipe affect the head in the entire system.
• Finally, I am not sure what you mean by ponds: are you planning on building water storage elements? Or do you refer to catch basins? In either case, I think you can use SWMM to model their hydraulic behavior.

Hope this helps!

Hi Felipe;

Thanks a lot for your answers and assessments. I think it was an important informations for both myself and other relevant project engineers.

I mean it is "drainage ponds" which use with outfall channels in road drainage projects. In a way, as you say this is a storage elements. I think it can be described and solved with your assessments which above.

Thanks.

Sorry, I could not tell from question that you were licensed engineer. Your question direction seems to be using the road system and access potential to develop water storage. Water storage can have many benefits, but also effects and liabilities. Installing ponds, dikes, dams, channel modifications are various forms of hydrological modifications. If volume of water storage is important, identifying preferential dam locations may be important. These modifications can affect various aquatic habitat and channel functions, water quality and sediment transport; benefits possible for water uses as irrigation, fire control, perhaps recreation, fishing, etc. As with any project with intent to modify hydrology, it is best that decision maker be presented with full assessment of effects to make informed decision and as well identify areas of mitigation or design concerns. The larger the drainage size (named stream, watershed, or basin scale), the more complex and detail may be needed. If rural areas are involved and downstream, failure of structures are unlikely to have same effects as if failure would flood downstream communities or urban areas. I would make sure I have reviewed drainage land use, geology, soils, rainfall and streamflow records. Below moderate to large dams, culverts and other crossings are unlikely to be sufficient unless specifically designed for bipass or overflow.

I would consult with fisheries biologists, botanists, etc. I would make sure equipment used is washed as needed to avoid transfer of invasive species. I would make sure ponds have overflow channel or armored to allow overflow. If roads are used to develop permanent ponds or lakes with control to manage flow, I would design road much like a dam, with clay core, compaction, etc., design armored overflow. It is not unusual for many US areas even with great hydrology data, for the design storm uncertainty to be plus or minus 40%. I am unfamiliar with storm severity data for Africa, but uncertainty can be a significant factor. For many large stream systems, providing for aquatic organism passage is an important concern, so if you are installing culverts, they need to be designed for outlet control, submerged. I am used to the team approach to projects, but consulting with a variety of expertise, specialists, landowners in vicinity can provide both benefits and perhaps frustrations, depending on your opinion, and the direction of decision maker or developer.

We use various methods to allow for dependent species and instream flows, depending on the circumstance. In most instanced we would recommend bankfull flow releases every year or two, to maintain channel capacity, and some use the 7Q10 flow as the minimum flow released from control structures to maintain perennial flow, in addition to any downstream needs with water rights.

There are guides on internet if needed to address not only road construction, design, but also size of sediment basin, plunge or scour pool, pond, dike, dam, culvert sizing nomographs, erosion control, etc. Some of your training and texts probably covered topics, but pulling it all together into project form to fit specific circumstance adds complexity. I have learned, especially in relative flat or inaccessible terrain, the value of LiDAR adds substantial topographic and channel detail, improves identification of hydrologic boundaries, georeferencing streams and estimating stream types and morphology. DEM Contour intervals of less than 1 meter may be available for improvement of draft design before field survey Confirmation.

Dear researchers;

Thanks for all answers and descriptions. These are very useful advice and comments for my project.

Best regards.