Well,

The boundary conditions mentioned in the question are ideal for flooding in areas with a rainy climate. see the attachment.

Regards

You might be interested in reviewing the Rosgen stream classification (www.wildlandhydrology.com) as it applies to your landscapes. Steep gradient channels are entrenched, with typically have narrow floodplain. Being able to recognize and develop bankfull flow and floodplain indicators helps to determine the likelihood and degree of flooding. Gullies are typically deeply entrenched, and as a result, the former valley surface is a terrace and seldom flooded except in conditions where gully bank failures can sometimes fill the channel with sediment and/or woody debris during severe events and cause local flooding. Modifying or re-engineering channels to reduce flooding seldom is achieved without developing other issues. Rosgen has found that if you take two times the bankfull depth at thalweg, and project that across the cross section, this may approximate a 50 year flood event. Land cover types, land use, susceptibility to severe rainfall events, certain landscape impacts as severe wildfire, dam failures, landslides, stream channelization and other factors can be factors that contribute to flooding. There is a substantial body of hydrological research from experimental watershed research that could be helpful.

Mountainous areas, especially the valleys, are the most dangerous at all !!

I failed to mention, that in many areas at the remote sensing to field evaluation levels, soils, tree species and understory plants can be helpful in differentiating floodplains and flood zones. Sometimes bottomland hardwoods are different from upland species. LiDAR can be a helpful tool in detecting extent of relatively flat areas along streams, and may help identify erosion or minor to major flood overflow channel patterns sometimes evident on the floodplain. In our 2015 paper, Andy Maceyka and I explained the utility of LiDAR in identifying and improving hydrologic boundaries and stream patterns in the Francis Marion National Forest, a fairly dense, subtropical coastal plain forest with mostly low gradient, marine terrace terrain. Of course, the LiDAR has been useful tool in other National Forest terrain from SC and Ga mountains, Piedmont, sand hills, ridge and valley physiographic areas. Past activities such as moving or straightening valley streams for farming, drainage ditches, channel modifications, agricultural terraces, beaver dams, defining slope breaks such as between floodplain and hill slope or stream bank. At the field to site level, soil scientists, hydrologists and botanists or associated focused training can be helpful in recognizing, identifying and mapping flood indicators.

As mentioned in my earlier remarks, recognizing and identifying the bankfull flood indicators can be helpful. Depending on the system, the bankfull flood is probably about the 1.5 year flood, but this can vary from maybe the 1 year to perhaps as high as 2 year flood. I have noticed that in some of the areas I work in with stream gauging data, the stream discharge at the bankfull flood is roughly 1/10th of the 100 year flood discharge, or one order of magnitude if using log paper to plot data. The bankfull flood occurs most years, and for many stream types, has indicators that can be recognized by hydrologists and geomorphologists, or those with this training including some engineers and others.

Recognizing and mapping floodplains can have major implecations in saving lives, as well as affecting property values for certain activities, etc. So it is worthwhile to collaborate as well as recognize limits and uncertainty involved. Depending on your intent, I would also recommend compiling past flood data to develop envelop curve of the maximums found by drainage area size. In data poor areas, this may not be possible. Without this type flood data, perhaps extreme rainfall data can be obtained and potentially useful in flood projections.

Many Thanks Bayan Hussien , William F. Hansen and Ahmad S. Yasien Al-Gurairy for your contribution. these few contributions will go a long way.

I am very much still open to recommended text and reference materials.

Well,

- https://unesdoc.unesco.org/ark:/48223/pf0000220870

- Special Issue "Flood Risk Assessments: Applications and Uncertainties"https://www.mdpi.com/journal/water/special_issues/flood_risk_applications_uncertainties

- https://www.c-ville.com/a-flood-in-the-mountains-50-years-later-nelson-county-remembers-camilles-devastation/

Regards

Hello Mr Emeka Ude

I agree with Mr Bayan Hussien

Best regard

Highland is an area of elevation as against low plains or lowland. They are not necessarily flood plains. Its surface (topsoil) or subsurface soil may have high infiltration tendency that is, low runoff coefficient which may reduce flood risk. It may as well consist impermeable (mountainous) surface with large runoff coefficient which will increase flood risk as well. Basically runoff coefficient factor is essential as it relates the amount of runoff to the amount of precipitation received. However, with topographical variation either with steep or gentle gradient the low plains will be susceptible to flooding if adequate storm water channels are not implemented.

Hence, conduct flood risk assessment as suggested by Bayan Hussien and then classify your study area. Source for contour map or generate a topo survey using GIS software.

I agree with Mr Bayan Hussein

I agree with Mr Bayan Hussein and Chibundu Jula. Conduct a flood risk assessment

Mountains.

If there are flood risks, there is need to construct a dam to reduce the damage of floods.