ADAPTATION OF 1D AND 2D HYDRAULIC MODEL CALCULATION Location – Dimitrovgrad, SerbiaGeneral characteristics of the bed of river Nisava at the municipality ofDimitrovgradSection of Nisava river, from the border with the Republic of Bulgaria to the border ofthe municipality of Dimitrovgrad has a length of 13.035 km, ie. from 130+350.50 to km143+380.50.In the city center Dmitrovgrad, from km 135+630 to km 136+880, River Nisava isregulated. Cross section of the regulated channel is trapeze, with the followinggeometrical characteristics:• Bottom width - b = 12.00m;• Height of minor bed - h 4.00m;• In certain sections minor riverbed ends within the embankment, with height h = 1.0m;• Longitudinal decline of the level of bottom of regulated channel is Jo = 0.3%.Bandwidth of regulated bed is provided for the flow probabilities P = 1% -. Figure 1For the slope protection of regulated channel on the concave banks, it is providedtheir encasement with extruded crushed stone, with thickness d = 25-30cm andheight h = 2.0m. On other sections slopes of the regulated channel are protected bybiotechnical work-appropriate seeding grasses.In the section where regulation works were carried out, regulated bed is in goodcondition. The banks are stable and covered with low grass. However, on the convexcurves, and partly on the straight sections it results in the formation of significantreefs, which are visible also at high water levels, which indicates that the bottomwidth of regulated minor troughs of b = 12m is overestimated, Figure 1 andphotographs 1 and 2. Obloga, redjan lom. kamen d=25-30cm 1:2 4.5 Nozica 0 1:23.66 V=1.0m3/m 2.00 3 V=1.0m /m 7.30 12.00 7.30 Figure 1 Typical cross section of the regulated riverbed of the river Nisava in Dimitrovgrad
Photos 1. Regulated riverbed Nišava in Dimitrovgrad Photo 2 Bank fortification on the left concave bank and shoal on the right bank, upstream end of regulation works carried out in Dimitrovgrad, km 136 +880Photo 3. Regulated riverbed Nisava, bifurcation flow in the center of Dimitrovgrad
In the section upstream from Dimitrovgrad to the border with Republic of Bulgaria,river Nisava flows through several hundred meters wide river valley. The valley isformed in sandy clay and loam, on the surface is humus layer and presents asignificant arable land in this area. Major bed of the river is on the left bank limitedwith local road route and the route of the international railway and road. On the rightbank, slightly undulating river valley is extending, and it is 100-600m wide.Riverbanks are low, and inundation areas are threatened by high waters of the riverNisava. Minor riverbed is cut into the sandy - silty - clay material on the banks, withthickness of 1.5 - 2m, and on the bottom are expressed troughs of sand and gravel,photos 4 and 5. Riverbanks are covered with small, and locally large plants, and onsections where vegetation does not exist, erosion and destruction of riverbanks areexpressed. Photo 4. Right banks of the Nisava river upstream from Dimitrovgrad, Sector IV, The riverbed is cut into the sandy-argillaceous material, larger fractions of sand and gravel are at depths of 1.5 - 2.0m, reefs in the riverbed Photo 5. The appearance of inundation on the right bank, sector IV, demolition of the concave right bankUpstream of Dimitrovgrad regulation works have been derived in the previous periodon the section of approximately 700m length, downstream of the pedestrian bridge
on piles. Cross section of the regulated channel is trapeze, with the followinggeometrical characteristics: • Bottom width of minor river bed b = 7.00m; • Height of minor bed h = 1.00m; • Height of major bed h = 2.20m; • Forland width bf = 1.0m;Major riverbed is completed with embankment, the embankment crown width isbn=1.0m, and height h 1.0m. Embankment height and bandwidth of the projectedregulated riverbed is determined by the computation of water level for the reliableflow of probabilities P = 2%, Figure 2 Longitudinal decline of the level of bottom ofregulated channel in the whole section is Jo = 0.45%.Derived regulation works - bank fortification of locally and orderly crushed stone onconcave banks and embankment on the right bank, are in relatively good condition.In this section, to ensure the flow profile it is necessary only cleaning minor bed offine and coarse vegetation, photos 6 and 7. In relation to the projected flow profileFigure 2, the distance between the roots of the embankment and the edge of theminor bed is 5-8m, photo 7. Obloga, grubo sredjen 1 1: lom. kamen d=30-50cm 1: 1:2 2.20 1 Nozica 1:2 1: 1 V=1.0m3/m . 5 .5 1: 1 1.0 1.0 1.0 4.40 1.0 1.5 7.00 1.5 1.0 4.40 1.0Figure 2 Typical cross section of the regulated riverbed upstream from DimitrovgradNišavaPhoto 6. Performed works in the bridge zone number 2, bank fortification of crushed aligned stone d50cm
Photo 7. Regulated riverbed Nisava derived regulation works downstream of the bridge on the right concave bank, left bank is covered with dense vegetationThe main results of hydraulic calculations which are allowed from the simulationmodel HEC RAS, are shown in Tables 1, 2 and 3 and the graphs 1, 2 and 3.Flood zone for the reliable computation flow Q1% are shown on a topographic map ofR = 1:25000, graphic Attachment 1. The topographic map with cadastral situationand flood zones, is also shown, graphic Annex 2. Figure 3 Cross section of the riverbed Nisava and computational level of water at a flow Q1% Q2% Q5%, the sector I, Pr 2 (47) - km 130 +358.80
Figure 4 Calculating levels of water at a flow Q5%, Q2%, Q1%, profile Pr 54 (24) - km 136 +090.80, Sector II Figure 5 Calculating levels of water at a flow Q5%, Q2%, Q1%,the profile of the bridge no.4 – 136+392.0 , the main part of the course and branches, Sector IIIIn this sector on the right bank, are located facilities for water supply, as well asimportant agricultural lands and residential and agricultural facilities, Drawings 1 and2, Figures 7 and 8.
Figure 6 Calculating levels of water at a flow Q5% Q2% Q1% profile Pr 88 (191) – km 137+579.20 , Sector IVFigure 7 Calculating levels of water at a flow Q5% Q2% Q1%, the water intake area, profile Pr 97 (137) - 139 +060.7 km, Sector IV